I have created a drools "core" plugin that allows me to incorporate Drools into an RCP. However, since doing so, the Eclipse tools for Drools do not work properly, and there is indication of an error in the drl file. Nevertheless, I can edit the file, the RCP runs with the new rules, etc. In my plugins, I have the main eclipse drools feature and plugin; in my workspace I have the core drools project that contains the compiler, core, and limited dependencies. I have also exported the latter plugin, and dragged it into my eclipse installation. Do these three different things foul each other up? Right now I do not use a separate target for my RCP compilation, but just the main IDE installation. Very sorry if this is completely stupid - I am actually ecstatic that I finally got the drools engine incorporated successfully into my RCP. But the IDE is sure upset. Here is the trace when I try to save the altered drl file (which does, in fact, save successfully despite the trace): !ENTRY org.eclipse.ui.workbench 4 2 2007-11-24 15:08:07.096 !MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench". !STACK 0 java.lang.NullPointerException at org.drools.eclipse.util.ProjectClassLoader.getRawLocationFile(Unknown Source) at org.drools.eclipse.util.ProjectClassLoader.getRawLocationURL(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools.eclipse.util.ProjectClassLoader.getProjectClassLoader(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.generateParsedResource(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.parseResource(Unknown Source) at org .drools .eclipse.editors.outline.RuleContentOutlinePage.initRules(Unknown Source) at org .drools.eclipse.editors.outline.RuleContentOutlinePage.update(Unknown Source) at org .drools .eclipse.editors.outline.RuleContentOutlinePage.createControl(Unknown Source) at org .eclipse .ui .views.contentoutline.ContentOutline.doCreatePage(ContentOutline.java: 135) at org.eclipse.ui.part.PageBookView.createPage(PageBookView.java:399) at org.eclipse.ui.part.PageBookView.partActivated(PageBookView.java: 741) at org .eclipse .ui .views .contentoutline.ContentOutline.partBroughtToTop(ContentOutline.java:210) at org.eclipse.ui.internal.PartListenerList $2.run(PartListenerList.java:87) at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37) at org.eclipse.core.runtime.Platform.run(Platform.java:857) at org .eclipse.ui.internal.PartListenerList.fireEvent(PartListenerList.java: 57) at org .eclipse .ui .internal.PartListenerList.firePartBroughtToTop(PartListenerList.java: 85) at org .eclipse.ui.internal.PartService.firePartBroughtToTop(PartService.java: 87) at org .eclipse .ui .internal .WorkbenchPagePartList.firePartBroughtToTop(WorkbenchPagePartList.java: 75) at org .eclipse .ui .internal .WorkbenchPagePartList .fireActiveEditorChanged(WorkbenchPagePartList.java:51) at org.eclipse.ui.internal.PartList.setActiveEditor(PartList.java:152) at org .eclipse.ui.internal.WorkbenchPage.makeActiveEditor(WorkbenchPage.java: 1224) at org .eclipse.ui.internal.WorkbenchPage.updateActivePart(WorkbenchPage.java: 1169) at org.eclipse.ui.internal.WorkbenchPage.partAdded(WorkbenchPage.java: 1583) at org .eclipse.ui.internal.EditorAreaHelper.addEditor(EditorAreaHelper.java: 210) at org .eclipse.ui.internal.EditorManager.createEditorTab(EditorManager.java: 774) at org .eclipse .ui.internal.EditorManager.openEditorFromDescriptor(EditorManager.java: 673) at org.eclipse.ui.internal.EditorManager.openEditor(EditorManager.java:634) at org .eclipse .ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java: 2737) at org .eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java: 2651) at org.eclipse.ui.internal.WorkbenchPage.access$13(WorkbenchPage.java: 2643) at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java: 2595) at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java: 67) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2590) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2574) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2565) at org.eclipse.ui.ide.IDE.openEditor(IDE.java:644) at org.eclipse.ui.ide.IDE.openEditor(IDE.java:603) at org .eclipse .jdt .internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java: 286) at org .eclipse .jdt .internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java: 139) at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:194) at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:175) at org .eclipse .jdt .ui .actions .SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:268) at org .eclipse .jdt .ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java: 244) at org .eclipse .jdt .internal .ui .packageview .PackageExplorerActionGroup.handleOpen(PackageExplorerActionGroup.java: 316) at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart $5.open(PackageExplorerPart.java:613) at org.eclipse.jface.viewers.StructuredViewer $2.run(StructuredViewer.java:820) at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37) at org.eclipse.core.runtime.Platform.run(Platform.java:857) at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:46) at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:199) at org .eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java: 818) at org .eclipse .jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1079) at org.eclipse.jface.viewers.StructuredViewer $6.handleOpen(StructuredViewer.java:1183) at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:263) at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:257) at org.eclipse.jface.util.OpenStrategy $1.handleEvent(OpenStrategy.java:297) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:66) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1495) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1519) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1504) at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1295) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3350) at org.eclipse.swt.widgets.Control.sendTrackEvents(Control.java:2734) at org.eclipse.swt.widgets.Control.kEventControlTrack(Control.java: 1953) at org.eclipse.swt.widgets.Widget.controlProc(Widget.java:367) at org.eclipse.swt.widgets.Display.controlProc(Display.java:835) at org.eclipse.swt.internal.carbon.OS.CallNextEventHandler(Native Method) at org.eclipse.swt.widgets.Tree.kEventMouseDown(Tree.java:2363) at org.eclipse.swt.widgets.Widget.mouseProc(Widget.java:1262) at org.eclipse.swt.widgets.Display.mouseProc(Display.java:2819) at org.eclipse.swt.internal.carbon.OS.SendEventToEventTarget(Native Method) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2938) at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2389) at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2353) at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2219) at org.eclipse.ui.internal.Workbench$4.run(Workbench.java:466) at org .eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java: 289) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java: 461) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) at org .eclipse .ui.internal.ide.application.IDEApplication.start(IDEApplication.java: 106) at org .eclipse .equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:169) at org .eclipse .core .runtime .internal .adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:106) at org .eclipse .core .runtime .internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:76) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 363) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 176) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun .reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java: 39) at sun .reflect .DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java: 25) at java.lang.reflect.Method.invoke(Method.java:585) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:508) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:447) at org.eclipse.equinox.launcher.Main.run(Main.java:1173) !ENTRY org.eclipse.ui.workbench 4 2 2007-11-24 15:08:07.523 !MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench". !STACK 0 java.lang.NullPointerException at org.drools.eclipse.util.ProjectClassLoader.getRawLocationFile(Unknown Source) at org.drools.eclipse.util.ProjectClassLoader.getRawLocationURL(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools.eclipse.util.ProjectClassLoader.getProjectClassLoader(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.generateParsedResource(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.parseResource(Unknown Source) at org .drools .eclipse.editors.outline.RuleContentOutlinePage.initRules(Unknown Source) at org .drools.eclipse.editors.outline.RuleContentOutlinePage.update(Unknown Source) at org .drools .eclipse.editors.outline.RuleContentOutlinePage.createControl(Unknown Source) at org .eclipse .ui .views.contentoutline.ContentOutline.doCreatePage(ContentOutline.java: 135) at org.eclipse.ui.part.PageBookView.createPage(PageBookView.java:399) at org.eclipse.ui.part.PageBookView.partActivated(PageBookView.java: 741) at org.eclipse.ui.internal.PartListenerList $1.run(PartListenerList.java:72) at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37) at org.eclipse.core.runtime.Platform.run(Platform.java:857) at org .eclipse.ui.internal.PartListenerList.fireEvent(PartListenerList.java: 57) at org .eclipse .ui.internal.PartListenerList.firePartActivated(PartListenerList.java: 70) at org.eclipse.ui.internal.PartService.firePartActivated(PartService.java: 73) at org.eclipse.ui.internal.PartService.setActivePart(PartService.java: 171) at org .eclipse .ui .internal .WorkbenchPagePartList .fireActivePartChanged(WorkbenchPagePartList.java:56) at org.eclipse.ui.internal.PartList.setActivePart(PartList.java:126) at org.eclipse.ui.internal.WorkbenchPage.setActivePart(WorkbenchPage.java: 3402) at org.eclipse.ui.internal.WorkbenchPage.activate(WorkbenchPage.java: 611) at org .eclipse .ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java: 2748) at org .eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java: 2651) at org.eclipse.ui.internal.WorkbenchPage.access$13(WorkbenchPage.java: 2643) at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java: 2595) at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java: 67) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2590) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2574) at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java: 2565) at org.eclipse.ui.ide.IDE.openEditor(IDE.java:644) at org.eclipse.ui.ide.IDE.openEditor(IDE.java:603) at org .eclipse .jdt .internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java: 286) at org .eclipse .jdt .internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java: 139) at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:194) at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:175) at org .eclipse .jdt .ui .actions .SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:268) at org .eclipse .jdt .ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java: 244) at org .eclipse .jdt .internal .ui .packageview .PackageExplorerActionGroup.handleOpen(PackageExplorerActionGroup.java: 316) at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart $5.open(PackageExplorerPart.java:613) at org.eclipse.jface.viewers.StructuredViewer $2.run(StructuredViewer.java:820) at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37) at org.eclipse.core.runtime.Platform.run(Platform.java:857) at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:46) at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:199) at org .eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java: 818) at org .eclipse .jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1079) at org.eclipse.jface.viewers.StructuredViewer $6.handleOpen(StructuredViewer.java:1183) at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:263) at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:257) at org.eclipse.jface.util.OpenStrategy $1.handleEvent(OpenStrategy.java:297) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:66) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1495) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1519) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1504) at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1295) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3350) at org.eclipse.swt.widgets.Control.sendTrackEvents(Control.java:2734) at org.eclipse.swt.widgets.Control.kEventControlTrack(Control.java: 1953) at org.eclipse.swt.widgets.Widget.controlProc(Widget.java:367) at org.eclipse.swt.widgets.Display.controlProc(Display.java:835) at org.eclipse.swt.internal.carbon.OS.CallNextEventHandler(Native Method) at org.eclipse.swt.widgets.Tree.kEventMouseDown(Tree.java:2363) at org.eclipse.swt.widgets.Widget.mouseProc(Widget.java:1262) at org.eclipse.swt.widgets.Display.mouseProc(Display.java:2819) at org.eclipse.swt.internal.carbon.OS.SendEventToEventTarget(Native Method) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2938) at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2389) at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2353) at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2219) at org.eclipse.ui.internal.Workbench$4.run(Workbench.java:466) at org .eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java: 289) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java: 461) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) at org .eclipse .ui.internal.ide.application.IDEApplication.start(IDEApplication.java: 106) at org .eclipse .equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:169) at org .eclipse .core .runtime .internal .adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:106) at org .eclipse .core .runtime .internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:76) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 363) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 176) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun .reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java: 39) at sun .reflect .DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java: 25) at java.lang.reflect.Method.invoke(Method.java:585) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:508) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:447) at org.eclipse.equinox.launcher.Main.run(Main.java:1173) !ENTRY org.eclipse.ui 4 4 2007-11-24 15:08:48.763 !MESSAGE Save Failed !ENTRY org.eclipse.ui 2 0 2007-11-24 15:08:48.764 !MESSAGE Save Failed !STACK 0 java.lang.NullPointerException at org.drools.eclipse.util.ProjectClassLoader.getRawLocationFile(Unknown Source) at org.drools.eclipse.util.ProjectClassLoader.getRawLocationURL(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools .eclipse.util.ProjectClassLoader.getProjectClassPathURLs(Unknown Source) at org .drools.eclipse.util.ProjectClassLoader.getProjectClassLoader(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.generateParsedResource(Unknown Source) at org.drools.eclipse.DroolsEclipsePlugin.parseResource(Unknown Source) at org .drools .eclipse.editors.outline.RuleContentOutlinePage.initRules(Unknown Source) at org .drools.eclipse.editors.outline.RuleContentOutlinePage.update(Unknown Source) at org.drools.eclipse.editors.AbstractRuleEditor.doSave(Unknown Source) at org.drools.eclipse.editors.DRLRuleEditor.doSave(Unknown Source) at org.drools.eclipse.editors.DRLRuleEditor2.doSave(Unknown Source) at org.eclipse.ui.internal.SaveableHelper$1.run(SaveableHelper.java: 143) at org.eclipse.ui.internal.SaveableHelper$4.run(SaveableHelper.java: 266) at org .eclipse .jface.operation.ModalContext.runInCurrentThread(ModalContext.java:369) at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:313) at org.eclipse.jface.window.ApplicationWindow $1.run(ApplicationWindow.java:758) at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java: 67) at org.eclipse.jface.window.ApplicationWindow.run(ApplicationWindow.java: 755) at org.eclipse.ui.internal.WorkbenchWindow.run(WorkbenchWindow.java: 2451) at org .eclipse .ui .internal .SaveableHelper.runProgressMonitorOperation(SaveableHelper.java:274) at org .eclipse .ui .internal .SaveableHelper.runProgressMonitorOperation(SaveableHelper.java:253) at org.eclipse.ui.internal.SaveableHelper.savePart(SaveableHelper.java:148) at org.eclipse.ui.internal.EditorManager.savePart(EditorManager.java: 1345) at org.eclipse.ui.internal.WorkbenchPage.savePart(WorkbenchPage.java: 3202) at org.eclipse.ui.internal.WorkbenchPage.saveEditor(WorkbenchPage.java: 3215) at org.eclipse.ui.internal.SaveAction.run(SaveAction.java:73) at org.eclipse.jface.action.Action.runWithEvent(Action.java:498) at org .eclipse .jface .action .ActionContributionItem .handleWidgetSelection(ActionContributionItem.java:546) at org.eclipse.jface.action.ActionContributionItem.access $2(ActionContributionItem.java:490) at org.eclipse.jface.action.ActionContributionItem $6.handleEvent(ActionContributionItem.java:443) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:66) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1495) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1519) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1504) at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1295) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3350) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2954) at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2389) at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2353) at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2219) at org.eclipse.ui.internal.Workbench$4.run(Workbench.java:466) at org .eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java: 289) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java: 461) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) at org .eclipse .ui.internal.ide.application.IDEApplication.start(IDEApplication.java: 106) at org .eclipse .equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:169) at org .eclipse .core .runtime .internal .adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:106) at org .eclipse .core .runtime .internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:76) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 363) at org .eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java: 176) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun .reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java: 39) at sun .reflect .DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java: 25) at java.lang.reflect.Method.invoke(Method.java:585) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:508) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:447) at org.eclipse.equinox.launcher.Main.run(Main.java:1173)