I now have eight usergroups that have been added, all of them are named "Default", all of them have a "delete" link. When I try to delete any of them, the message "You can't delete this usergroup." appears.
I've tried all of the fixes that have been posted, even installed a new copy of "adm-misc.php", nothing works.
What exactly is the fix here? Also, when adding a new usergroup, the page redirects to a blank page.