[rules-users] working memory error

I have two knowledge bases,one is drl file the other is pkg file. My application creates knowledge base from drl files first then create knowledge base from pkg file. There is nothing wrong when I create drl file knowledge base and fire rules, but I got below error when I create pkg file knowledge and fire the rules. Does anyone know what this issue mean? Caused by: java.lang.LinkageError: loader constraint violation: loader (instance of org/drools/rule/JavaDialectRuntimeData$PackageClassLoader) previously initiated loading for a different type with name "org/drools/WorkingMemory" -- View this message in context: http://drools.46999.n3.nabble.com/working-memory-error-tp3961517.html Sent from the Drools: User forum mailing list archive at Nabble.com.