When debug messages are allowed WP displays
Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead.
That's from using user level 8 on line 18 - should be 'administrator' I guess...
btw, one more warning -
Notice: Undefined variable: operation in .../wp-content/plugins/rvg-optimize-database/rvg-optimize-db.php on line 97 (presumably a totally abandoned line of code?)