I've found a problem (probably a bug in mvel) running drools expert 5.5. The MessageSourceElement constructor uses variable arguments: public MessageSourceElement(Enum<?> enumerationElement, Object... parameters) { My drl contains a method with consequence: then insert (new MessageSourceElement(ValidationException.MESSAGE_LIST.USER_CANT_OVERRIDE_THEMSELVES, new Object[]{})) end If I manually create the array of objects and pass it to the constructor it works correctly, but if I try to use variable parameters: insert (new MessageSourceElement(ValidationException.MESSAGE_LIST.USER_CANT_OVERRIDE_THEMSELVES)) insert (new MessageSourceElement(ValidationException.MESSAGE_LIST.USER_CANT_OVERRIDE_THEMSELVES, something, somethingElse)) I experince a very strange behavior: The first time the rule executes properly, but any subsequent execution fails with RuntimeException "cannot invoke method" ArrayIndexOutOfBoundsException 1 This happens because the second time mvel tries to call the two parameters constructor (Enum, Object[]) no matter what the real constructor we are trying to use (Enum), (Enum, SomeObject, SomeAnotherObject) and fails when trying to extract the parameters by reflection. I don't know if this is a known bug or if it should be reported, I hope it will save some time someone. -- View this message in context: http://drools.46999.n3.nabble.com/RuntimeException-cannot-invoke-method-A... Sent from the Drools: User forum mailing list archive at Nabble.com.