SQL 2005 Add New Login Fails Error Msg 15025.

I have read alot of threads her about 15025 and not one of them have addressed my problem or solved it.

I wanted to add a user to a new database, when I go to security and logins her login is not in the system, yet she was able to log into the production db and do her job without any problems using Windows Domain account.

I went to the New Login and tried to add the record but it gave me an error that the DomainUserName already existed error 15025.

I have gone into every database on the server to see if the login was in any of them and it was not. Then I tried to find orphan users and did find one in about 1/2 the databases that was from our Software provider.

My guess is there is a sid issue, but I am at a loose how to find it or fix it so I can add them to other db's.

I did run these commands

execute as login = 'DomainUserLogin'
-- Completed Sucessfully

select suser_name()
-- Returned the DomainUserLogn

I am using the Managment Student to manage the users.