I could not reproduce your error on my own installation, so you can go to Webpanel Settings and click Clear Cache to see if that fixes it.
The fix does work for me, but only for newly added bans. To fix old bans you will have to run this query from phpMyAdmin (make a backup of sb_bans first just to be safe):
Code:
UPDATE sb_bans SET country = NULL WHERE country = "zz"