After formatting and reinstalling a client PC, and using a different NIC when installing the WHS Connector software, I two listings for the same PC (same computer name). An examination of the Registry on the server indicated that since the MAC address was different, it appears to have treated it as a different PC. The old entry showed the PC as unavailable and there is no way in the GUI that I could find to remove that entry and its associated backup files. Manually removing the old PC's entry in the Registry at:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Home Server\Transport\Clients
and rebooting the server removed the entry, but the original backup space is probably being taken up.
There needs to be a GUI option/method of removing a specific PC and free up its associated backup space.
I had this exact same problem. A more active interface for the server under a special admin password, etc, would sure make it easier. My server is in the basement, and it's a pain to bring it upstairs just to do a little cleanup.
As requested, it is running with no monitor, keyboard or mouse, so the interface is the lifeline. Great product, but I'm sure others will do like I did, and rebuild machines and make changes.