This is just off the top of my head but it could be that you're including global.php in twice. Since DB_Sql_vb is already defined (possibly through config.php) including it again will bring up that error.
If you delete that file see what happens... or if it's not that, try to look for a file that is referenced twice by require -- that's probably you're answer
I do not know if the mysql error is related to the first one, but could be!
--red