An Office service that supports add-ins to interact with objects in Office client applications.
I just had and solved this problem, the issue for me was that the username was to long for the "User Logon name (tre-Windows 2000)" field which is 20 characters.
The "CreateUser" function unfortonatly uses one field "Username" for both the modern "User logon name" and the pre 2000 one.
Hope this helps.