arctain

All,

I have upgraded from DNN 3012 to 3013 and am getting this same error. While the deletion of the "not fully registered" users does resolve the  "users accounts not accessible" hard error, it does not resolve the error with registering new users. The SuperUser account has not been deleted, and rolling back to 3012 does resolve the error. At this point (after upgrading to DNN 3013) new users cannot be added without causing an error.

I don't have any problem adding users to my upgraded sites.  It would be interesting to find out what is different about your environment.