could you attach complete stack trace as that might tell us more.
Sorry, i lost application server logs after log rotation but i finally found the problem and would like to share the solution. Error message and exception were a bit misleading, there was a problem with variables declaration. I have used a local variable in a script task with the same name as a global variable declared in another process. Clearly when i was unit testing process problem was hidden because i was loading only one process in knowledge base. By the way after checking and renaming local variables problem as been solved.
I have the same problem.
But problem is not duplicate variable duplicate names nor variable types.
I try to create different processes but I have still the same problem.