Hello
Well I dont know a lot about this sort if thing but I think I had the same problem with mine. Whenever I copied music from CDs onto the player it said "unknown format" but anything else worked fine. I copied it straight off of Windows Media player and it didn't work so then I tried copying the music directly from the files on my computer and it seems to have worked.
I hope that helps your problem.
Sorry if it doesn't make sense though. I really dont know a lot about this sort of thing.
sarah
June 2008