I've seen the same problem with Hypersonic.
It happens when I start JBoss under a normal profile.
When I start JBoss from root it works.
Must be an authority/configuration problem.
If you locate the config change let me know.
I have found my mistake. I thought, adding the postgres jar to my CLASSPATH was enough. I found that adding the jdbc** .jar to the lib/ext directory solved my problem.
Such an easy solution, but i was not expecting something like the classpath. A class not found error would have helped much.
Thanks for listening