Because I am running Windows Server Enterprise 2008 on my Laptop with Hyper-V enabled, I continuously Remote Desktop to my Virtual Machine. Even for a domain admin in the guest, you have to have group policy configured to allow the Remote Desktop Users group to allow logon through terminal services. Here is where you do it:
Click Start, point to Run, type mmc, and then click OK.
On the File menu, click Add/Remove Snap-in.
In Add/Remove Snap-in, click Add, and then, in Add Standalone Snap-in, double-click Group Policy Object Editor.
In Select Group Policy Object, click Browse, browse to the Group Policy object (GPO) that you want to modify, click OK, and then click Finish.
Click Close, and then click OK.
In the console tree, click User Rights Assignment.