A weird lock-out

Very strange. Never heard of anything like this before. I would try the following after backing up your database:

1. Using phpMyAdmin, disable all the contributed and custom modules
   UPDATE system SET status = 0 WHERE type = 'module' AND filename LIKE 'sites/%'
2. The clear the cache tables:
   
   

    TRUNCATE TABLE cache;
    TRUNCATE TABLE cache_block;
    TRUNCATE TABLE cache_bootstrap;
    TRUNCATE TABLE  cache_field;
    TRUNCATE TABLE  cache_filter;
    TRUNCATE TABLE  cache_image;
    TRUNCATE TABLE  cache_menu;
    TRUNCATE TABLE  cache_page;
    TRUNCATE TABLE  cache_path;
   

   
   
   NOTE: cache_form was not included because it is not actually a cache table. It is actually a form_state table

3. Then run cron for the site
4. Then see if you can uninstall any of the modules at this point
5. Then run update.php for the site
6. Then see if you can enable the modules again.
   You might want to do this step one at a time to see if a particular module is the culprit of the 'lock-out'

As I said before, I've never actually encountered this type of error before and these are just the steps I would try. Hope this helps!