This is a weird problem. I think it has to do with a change in the database maybe. I built a new backend and installed mythbuntu 7.10 on it. I copied all the recordings off my old backend to the new backend and backuped and restoried the correct parts of the database to move the recordings. Now the old recordings play fine through the frontend on the new backend. But on all my other frontends (over the network) the old recordings wont play (error message below). The network frontends can play live TV and can play new recordings I make on the new backend.

All the old recordings show up on the network frontends' watch recordings screen. But when I try to play them the screen flashes black for half a second and goes back to the watch recordings screen. Here is the error message mythfrontend writes to the terminal:
2007-10-27 20:01:26.459 TV: Attempting to change from None to WatchingPreRecorded
2007-10-27 20:01:26.462 RemoteFile::openSocket(control socket): 
                        Could not connect to server "" @ port -1
2007-10-27 20:01:26.462 RemoteFile::openSocket(file data socket): 
                        Could not connect to server "" @ port -1
2007-10-27 20:01:26.462 RingBuffer::RingBuffer(): Failed to open remote file (myth://:/1051_20071026233500.mpg)
0: start_time: 2585.537 duration: 334.426
1: start_time: 2585.502 duration: 334.423