I tried to make own Jopr's plugin, but I have a little problems:
1. Even if plugin is built correctly (Skeleton or any other from SVN), Jopr don't see it. Upload by webpanel, manualy copy, click "Scan" button and nothing.
2. If I will restart Jopr (or restart computer) I cannot login. Only what I see is this message: "The backend data source is unavailable".
Sounds like your problems are due to the database you are using. Either rhq-server.properties doesn't have the database settings correct, or your database is down/not functioning.
Take a look in your server log file (<install-dir>/logs) and look at what error messages are occurring. That should help pinpoint the problem.