From a newsgroup post: "After our further research, we think this issue can be related to a security policy setting: Computer configuration -> Administrative templates -> Windows components -> Terminal Services\Licensing: License Server Security Group.
If the status is set to Enabled, a local group called Terminal Services Computers is created. The Terminal Server License Server grants licenses only to computers whose computer accounts are placed in this group. When the target computer is a domain controller, this group is a domain local group.
If the status is set to Disabled, the Terminal Server License Server issues a license to any computer that requests one. The Terminal Services Computers group is not deleted or changed in any way. This is the default behavior.
If the status is set to Not Configured, the Terminal Server License Server acts the same as if the status is set to Disabled.
If you did not add any clients to this group, any machine attempting to connect to the terminal server would be denied".