Upgrade from 2.0 - 2.1

[LadyBeth]

I'm receiving this error when attempting to upgrade:

Database error in vBulletin 3.6.4:

Invalid SQL:
ALTER TABLE ppgal_setting ADD PRIMARY KEY (varname);

MySQL Error : Duplicate entry 'gallery_allowreplies' for key 1
Error Number : 1062
Date : Monday, January 1st 2007 @ 11:05:55 AM
Script : ***
Referrer : ***
IP Address : ***
Username : ***
Classname : vb_database