Front Row stuck at "Loading ... Media Library" screen

I've been using an older Mac Mini running Snow Leopard as a media center, using Front Row on it to connect to the iTunes running on my newer Mac Mini running Mountain Lion.

This has worked well for ages, but recently when I try to connect to the remote iTunes via Sources on Front Row, I just get stuck at the screen that says :

Loading "<remote server> Media Library"...

And have the little spinny icon going around and around. It never seems to connect at all, no matter how long I leave it.

I've even tried connecting to iTunes on my MacBook Pro (also running Mountain Lion) - this used to work too, but now gives the same problem as described above.

Has anyone seen this before, or have any suggestions what I can do to fix this? I have already tried rebooting all machines involved as well as clearing out the ~/Library/Caches on all machines too.