One of my community fellows has reported a challenging case this evening, he been trying to add a user to Dynamics GP and unable to succeed with this operation, and the obvious cause for this message was that the user could be already added to your database and not added to your GP nor your SQL level logins but wasn’t the case, the message is showing on any name you selects and while running under the “sa” user.
When you create the user at the SQL level it creates with no issues, you only have a problem while creating the user from Dynamics GP, therefore I tried a fresh copy of Dynamics GP and tried to create users with no luck, been sure that the “sa” is a system administrator on the SQL level and the “sa” is the owner of the DYNAMICS and other companies databases.
Digging deeply into this I ran SQL profiler trace to see what’s going on and realized that everything is working as desired, I tried to create the user using the CREATE LOGIN command and it creates the user perfectly! But noticed upon creating the user by using the command that the returned message wasn’t “Command Completed Successfully” it was “Mail Queued”, where I looked further into this and realized that the customer was having a DDL Trigger on the server level that tracks the changes on the Logins and sends an email to the Administrators informing them about this change following the best practices! And this was the real cause behind the issue, it seems that GP wasn’t receiving the expected result from adding this user and been generating unknown error, disabling the trigger got this issue to be fixed!
Hope that this helps.