did you import a backup of tv-channels?sounds like a broken/corrupted database to me.But I think it has something to do with the radiochannels. After I deleted all the webradiochannels and tv channels I made a rescan of the tv channels and now the tv channels are working inside MP.
You are probably right. But I made a clean install of windows and MP twice. And the same problem occurred 1. and 2. time. So this must be a bug...