Problem with Sansa Express MP3 Player

[Joe Shmoe]

I have a Sansa Express MP3 Player. all was going fine with it until yesterday. All the tracks on it are wma files bought from the old Tesco downloads site apart from the tracks already on it when it came. Yesterday I downloaded a track from the new Tesco Digital site Which makes you download a download manager. When I put this on the player and tried to play it it said licence expired. gradually this has spread to every other track on the player except the ones originally on the player. The tracks still play on the computer in wmp.
I was going to remove the tracks and try putting them on again but looking at the file folders on the player is one that says wmp. Do I need to delete this as well as the tracks or leave it there? Any help appreciated.Thank You!
:-)

[Joe Shmoe]

By the way I did a Virus scan with AVG8. It showed no problems.:-D

[Joe Shmoe]

Also if this is any help I managed to burn the same tracks to a CD without any problems. So I think it is the player at fault.:-D