Everything looks OK to me, I have the same setup and it works. The only time I get that error is when the password is actually wrong. All I can suggest is, check the password in the DB for leading or trailing spaces and make sure the password is in the correct case (Oracle passwords are not case sensitive, but JBoss passwords are).
thanks for your reply. As I found out the problem lies elsewhere: the other-config is called in addition to my own. See thread "Why is auth.conf-other always called". Still no good solution :-( (I copied my config settings into other, too, so my ejbs get authenticated twice, but at least, it works).