ok i think that i isolated the problem
besides this package i also had a second package that contained the Entity classes. I didn't include them anywhere but ofcourse the Persistence Unit tries to create the tables (stupid me for forgetting this)
when i remove this package then the above posted codes seem to work.
i'll look into this package now to see what goes wrong there
[Message sent by forum member 'johnnyvdlaar' (johnnyvdlaar)]
http://forums.java.net/jive/thread.jspa?messageID=235021