[rules-users] Cryptic error message: org.drools.compiler.FunctionError@191394e

I have converted my 3.1 DRL to 4.0, think I have the dependencies worked out (removed antlr-30ea8.jar) and now I am getting a cryptic error message from the DRL compiler: Rules.getRuleBase. org.drools.compiler.FunctionError@191394e org.drools.rule.InvalidRulePackage: org.drools.compiler.FunctionError@191394e at org.drools.rule.Package.checkValidity(Package.java:412) at org.drools.common.AbstractRuleBase.addPackage(AbstractRuleBase.java:292) ... Am I missing something with the plugin, is my DRL so badly munged the compiler can't explain what's wrong, or what? Thanks, Scott