When a mod fails to uninstall, corrupts something it should not had or makes SMF unable to upgrade. Then the following instructions will help reset SMF, but preserve some important information like topics, posts and members. Warning, the following instructions deletes your currently installed mods and uploaded themes. If for any reason a different option might be available ask for support at the 1.1 support board or the 2.0 support board.
First
BACKUP ALL YOUR DATA!!!
Second
Download the large upgrade package of your forums version.
Third
Open the package and delete upgrade.php files.
Fourth
Delete everything in the forums directory except for the settings.php file and the attachments and avatars directory.
Fifth
Upload the package to the forums directory and unzip the files.