Having recently done and upgrade from a rather old DB to v7.0.1, I've encountered a few tables that cannot be deleted from SLX via DB manager. Examples are: USEROPTION (not the new USEROPTIONS ), and PROJECTPLUGIN
This article includes a script that drops the table and deletes records from the three SalesLogix schema meta data tables.
Here is a summary:
drop table YourTableName
delete from sectabledefs where tablename = 'YourTableName'
delete from joindata where fromtable = 'YourTableName' or totable = 'YourTableName'
delete from resynctabledefs where tablename = 'YourTableName'
Click here to download the sample code