No album art displayed on certain albums.

I recently upgraded from the Sony 4GB Walkman (NWZ-E436F) to the 8GB (NWZ-E438F). When I transfer all my albums from Windows Media Player 11 into the player, only certain album covers will display on the screen. I never had this issue with the NWZ-E436F. I have upgraded the firmware from version 1.00 to 1.02 but that did not resolve the issue. Any suggestions would be greatly appreciated. Thank you.