I posted about caching and after some more investigation it appears the problem lies in just refreshing the rulebase. I created a simple package that contains 1 excel decision table which has 1 rule [row] in it. I ran my application. Then rebuilt the package in the Guvnor and my application refreshed the rule base correctly. I have other packages which contain many 100 rules if not 1000 rules all based on multiple excel based decision tables. If I run my application, then rebuild the package in the Guvnor, my application throws the exception. RuleAgent(Assembly) EXCEPTION (Fri Feb 26 12:02:32 EST 2010): java.lang.ClassCastException: org.drools.util.ObjectHashMap cannot be cast to org.drools.reteoo.BetaMemory. Stack trace should follow. org.drools.RuntimeDroolsException: java.lang.ClassCastException: org.drools.util.ObjectHashMap cannot be cast to org.drools.reteoo.BetaMemory It appears the problem occurs where there are many rules. Any ideas? Thanks.