Hello Joram, I will try to provide the stacktrace tomorrow. The situation is the following. I've got a process definition with a couple of automated activities, a bunch of java classes mainly used to invoke Axis2 webservices and 2 tasks for users. The process definition is deployed with no problem. I have a webservice using the jBPM api to start a process instance. When the Tomcat server is freshly started and there is no process engine instance yet I call the webservice which tries to retrieve the process engine which is then created and stored. But the starting of the process fails and the exception telling that JpdlProcessDefinition cannot be cast to java.util.List is thrown. If I use the jBPM console afterwards to start a process instance this error does not show up but a different one since I cannot supply the process instance variables needed in the first and automated activity via the jbpm-console. Strangely afterwards I can start as many process instances as I want with using my webservice without problems and they all run without problem from start to end. I had trouble seeing more than the cast exception but as bwestrich stated there is normally an inner cause for this one but I could not locate one. I'll try to get the stacktrace. Is there something you shouldn't do within java classes invoked by activities in the process? For example regarding calls in the constructor or whatever? Thanks for any hints Sebastian View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4263755#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...