Help with WMA ID3 Synch Sony Walkman NW-A857

[Caterpillar]

Hi!
I have a Japanese model NW-857. I don't speak or read Japanese (first problem but I am learning fast). Its a good player but I have been having problems syncing WMA files from my PC using WMP (yes, I know, dont use WMP). System is Windows 7 64bit.
The first problem was that album artwork would not sync. I overcame this by downloading Mediamonkey and manually updating all the ID3 tags from the internet. I then reloaded all the albums (there are quite a few of them) onto my player from WMP. Artwork problem (largely) solved!
Next issue is proving trickier. The Album Artist / Artist tag does not display for most of the albums loaded onto the player. In its place are two Japanese characters which I would hazard a guess stand for "artist unknown": same for most tracks.
OK, so back to Mediamonkey. I removed the albums from the player again and tried syncing from Mediamonkey. Hey presto! Album artist tags mysteriously worked...(can anyone explain why?) but there is a catch: the tracks synced from Mediamonkey will not play on the player. An error message flags up on the screen (in Japanese - not sure what it says but might be a DRM error) and the player attemtps to restart the track to no avail until I put it out of its misery.
Can anyone offer a solution please? I am perilously close to actually sitting down and enjoying some excellent quality, noise cancelled playback. Surely this is a first for us MP3 player users!
Thanks