uh.. you shouldn't touch database directly, it might be something corrupted now. try to remove plugin completely, and look for options in wp_options table that starts with 'agca_' those are AG Custom Admin options and feel free to delete those if you find them after plugin deinstallation. Download fresh plugin copy 188.8.131.52 if you have latest WP version, or 1.2.5 for earlier WP versions, install it, clear cache and refresh page. This should work in 99% situations. If it's not, disable all other plugins, and try again. If this doesn't help than, only thing that comes up to my mind is that your WP installation is corrupted somehow.