http://www.vbulletin.com/forum/showpost.php?p=1647926&postcount=4
http://www.vbulletin.com/forum/showthread.php?postid=1647720
Somehow, a serious, but not destructive bug worked its way into 3.7.4. After modifying a user in the UserCP, you will receive a database error when saving the user. I have updated the affected file, includes/class_dm_user.php, in the 3.7.4 download. If you downloaded 3.7.4 previous to this message, please download it again and replace the file.