I have a similar issue this morning. One of the PCs in my bookmarked list was showing as offline. When I checked it (luckily it was a local one in the office) I found it had changed its TV ID suddenly to a 10-digit one.
But even with TV running, when I try to connect to that PC I get "reason unknown" and it won't connect. This seems to have started after last night's TV system maintenance.
edit: restarting TV on the target PC resolved the connection issue