If you get this error "The specified domain either does not exist or could not be contacted." when you try to log on to your Terminal Server / Remote Desktop, it might be caused by the fact that you're machine is not connected to the domain controller. Or as Noam describes, maybe you have changed your IP-address and the DC doesn’t know about it. Also maybe sure you check your AD for DNS issues. As a workaround, you can use the following steps to resolve this issue (or download the .REG here):
1. Click Start, click Run, type regedit, and then click OK.
2. Locate the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server
3. Click Edit, point to New, and then click DWORD Value.
4. In the New Value #1 box, type IgnoreRegUserConfigErrors, and then press ENTER.
5. Right-click IgnoreRegUserConfigErrors, and then click Modify.
6. In the Value data box, type 1, click Decimal, and then click OK.
7. Quit Registry Editor.
(source http://support.microsoft.com/kb/902336)