Quoted from "READ THIS FIRST" (my highlighting)
Try to keep your posts short but relevent.
1) Post relevent configurations, but not everything.
2) Post full exception traces (often the real exception is embedded at the
end of the stacktrace)
3) Look for relevent exceptions BEFORE the exception you are reporting.
Ok, fair enough Adrian, sorry for this newbie mistake.
I'll try to be more precise this time.
Meanwhile typing this post, I have just read carefuly the log file and discovered that I had accidently copied my ejb jar file also in the /deploy/jbossweb-tomcat41.sar directory, which caused the problem.
Now it works !
Sorry again for calling help while It was just about an unfotunate windows drag'n'drop.