Hello, my system is a timed automata with a single state, which is initial. Its invariant is true. I also added a clock c to the declarations. The system can be found under http://www1.inf.tu-dresden.de/~s5030296/system.xml If I check the query A<> c==3 I get this error message: com.uppaal.engine.EngineException: com.uppaal.engine.ServerException: CAUGHT EXCEPTION: pfed_t::operator -= not implemented I'm using Sun Java 6.0