No no, you don't need to trash it. That error means one of your module had that controller but somehow it is missing now but its entry is still in the database. The actual solution of it should be to get that file back but if you just want to make it working without that controller then go to the database and find ps_tab table and search for AdminPsMboTheme in the 'class_name' column and delete it from there, and respected entries from ps_tab_lang. But before doing this don't forget to take backup of those tables for your safe side. This should allow you to load rest of pages then.