Hmm... weird problem. I would suggest you to download a new copy of the windows media player 10 from the source site[microsoft] and install it again.
I had a problem with WMP 10 , i downloaded the english version, but it showed all greek , cant even change the language. I downloaded again, another pack, and it worked great. btw, no big difference between wmp9 and wmp 10.[more bugs i guess in the new version