Ok, I have been struggling with this error for days now. I am getting a NoClassDefFoundError: Could not initialize class org.drools.rule.builder.dialect.java.JavaDialect error. I understand that this is most likely a classpath problem but have done almost everything to try and resolve it. I have the drools-compiler-5.1.0.jar in my lib folder where all my other jars are (which successfully work btw) and adding this jar there resolves a packagebuilder error also. Does anyone have any idea? The JavaDialect.class files are in the jar if I open it with 7zip...so it's not like they are not there. I'm really at a loss with this one now.