I restarted the server to ensure the changes would be applied and logged into a remote desktop session. A colleague then logged in off his machine and it booted me out, sighting someone else had logged into this session.

After a number of searches through the remote desktop settings, it turns out that by default, Windows Server 2008 only allows one remote desktop user per session.

To change this, go to Administrative tools > Terminal Services Configuration and double click on the item “Restrict each user to a single session”. From this window, uncheck the “Restrict each user to a single session” box. Voila! 2 users remote desktop’ed in simultaneously.