Best answer by Ryan Yacobucci
Check that the user has been correctly installed into the nsusers table.
SSH into the XMC server and the run following commands:
select * from nsusers;
You should see all users that are currently authorized to login. If your username is not in this list then I would try to login with the username that is. There should at least be a "root" user.
Once in the application you can then create a new user in the XMC --> Administration --> Users tab.
If you can't login we'll need to manually inject a user into the table.