Hello, I have a project, that uses Drools 5.0.1. I have a class, called RuleFlowProcessor, that's used to apply some of my rules to the objects. The instances of RuleFlowProcessor with the identical configuration should be used by different threads, and i use following mechanism: I initialize one instance of RuleFlowProcessor, and the threads take copy of this instance, calling the 'clone()' method, which is not synchronized, and in which I just create new instance of RuleFlowProcessor and init it, using the same data. And therefore I get an exception: Exception in thread "Thread-91" [Error: incomplete statement: (possible use of reserved keyword as identifier: )] [Near : {... globals != empt ....}] ^ [Line: 0, Column: 0] at org.mvel2.MVELInterpretedRuntime.parseAndExecuteInterpreted(MVELInterpretedRuntime.java:153) at org.mvel2.MVELInterpretedRuntime.parse(MVELInterpretedRuntime.java:44) at org.mvel2.MVEL.eval(MVEL.java:514) although, all the resources (.drl and .rf files) are parsed perfectly, when I use just one thread. In actions of my ruleflow, the dialect: 'mvel' was set by default, if I set dialect to 'java' without modifying any code, the error doesn't occur. The full stacktrace is in attach. I can send the project, that reproduces the problem, if needed. Best regards, Grigoriy Grigoriev.