Hi I am writing a drools based app. I am getting this error when I create an instance of KnowledgeBuilder at line, KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); Here is the error. Can anyone tell what does this error mean ? java.lang.NullPointerException: Parent ClassLoader may not be null at java.lang.ClassLoader.<init>(ClassLoader.java:239) at java.lang.ClassLoader.<init>(ClassLoader.java:226) at org.drools.util.CompositeClassLoader.<init>(CompositeClassLoader.java:38) at org.drools.util.ClassLoaderUtil.getClassLoader(ClassLoaderUtil.java:27) at org.drools.compiler.PackageBuilderConfiguration.setClassLoader(PackageBuilderConfiguration.java:333) at org.drools.compiler.PackageBuilderConfiguration.init(PackageBuilderConfiguration.java:165) at org.drools.compiler.PackageBuilderConfiguration.<init>(PackageBuilderConfiguration.java:159) at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:210) at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:143) at Org.drools.builder.impl.KnowledgeBuilderFactoryServiceImpl.newKnowledgeBuilder(KnowledgeBuilderFactoryS at org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder(KnowledgeBuilderFactory.java:47) at com.ts.DBconnector.readKnowledgeBase(DBconnector.java:125) I also tried adding this Thread.currentThread().setContextClassLoader( this.getClass().getClassLoader() ); But am still getting the same error ... please help ! -abhay