i'm guessing you have tried restarting the server? It seems that the plugin is finding your sourcebans entry in the database properly, but still thinks its using default SQL admins, which means it hasn't found sourceban's cvar yet.
For the record, your loyal database and sourcebans database(or sourcemod) can be completely separate, and the plugin should be capable of detecting your setup on its own. If you have not done so already restart your server and let me know how it goes. I run it with sourcebans, and have not encountered this error before
P.S. are there any other errors or message in the logs at all regarding loyalty?