well, the exception type is of course known to me and it is strange that this error happened. And it also tested on previously worked demo. Is there something special to do? I am using jar libraries always, it is a simple routine. But maybe there is really something passed through. We'll see.
Sometimes simple recompilation after cleaning can help. Though I made it several times and in this case it didn't help.
I will continue tests tomorrow too also and write back if this strange error will be solved.