I have read the same problem in this link: http://www.dotnetnuke.com/Community/ForumsDotNetNuke/tabid/795/forumid/108/threadid/46495/scope/posts/Default.aspx

and I have used this sql script with no result:

DECLARE @IUserID INT

SELECT @IUserID = UserID FROM USERS WHERE UserName = 'user name'
DELETE FROM USERPORTALS WHERE UserId = @IUserID
DELETE FROM USERROLES WHERE UserId = @IUserID
DELETE FROM USERSONLINE WHERE UserId = @IUserID
DELETE FROM PROFILE WHERE UserId = @IUserID

I have found another scipt to use but I am a newbie and I'm not able to use it:

CREATE procedure [dbo].[sp_DeleteUser_WithDependancies]
(
@UserName varchar(50)
)
as
begin

BEGIN TRAN

declare @UserId int
declare @AspNetId varchar(50)

set @UserId = (select UserId from users where username = @UserName)
set @AspNetId = (select UserId from AspNet_Users where username = @UserName)

print 'Deleting UserId:'+cast(@UserId as varchar(20))+' Guid:'+@AspNetId

It is better to just remove the authorization flag but keep the user indefinitely. 

There are so many dependancies that you will always have difficulty deleting users properly.
Your store procedure won't work because it does not cover all tables that need cleaning.

VERSION 4.7

This is the third time I have had this problem. I have 2 users who were editing their page. A error occured ( of course they could not remember ) . Then all of their normal view rights were gone. They could not see any content in any page but they could see the containers. When I went in as admin and tried to delete them I get "Error Deleting user. And the user is not DELETED. I though after the first one it was nothing to worry about, Now I have had 2 more in the past 2 days. Something while their page edits are saving is corrupting the user tables somewhere. Not versed enough to find the actual table corrupted

Any IDEAS