The local policy of this computer does not allow you to log on interactively.
This computer is the backup domain controller. I'm pretty sure this explains why I am unable to find the local policy to add this user because it is not visible under Computer Management. I also can't add users when you right click My Computer, choose Properties, and go to the Remote Tab. Under there you can specify users allowed to log onto the server, but the button is greyed out.
I have tried changing some of the users Active Directory Member settings, but I have not found one that works (Although, I'm quite sure Administrator works ;-)).
Thanks in advance for all of your help.