JBoss 4.0.4 not support Java 6. Migrate to a newer JBoss version.
Daniel, Thanks a lot for the answer.
The 'confusing' thing is that this application works without any problems when running with 'java' but not with 'javaws'.
So I was just wondering maybe somebody encountered this problem with web start and has a workaround/solution.
Of course upgrading the JBoss is an ideal solution but its not that easy in my case.
If you can't migrate JBoss AS version then keep using Java 5.
Precisely the problem is with javaws, this services is incompatible with Java 6.