QUOTE (RobG @ Jan 3 2010, 12:14)

... I'm using mp3tag in conjunction with a Cowon S9 player. Some of you may know that the S9 only displays album art sorted by album name not album artist which is what I want. ...
Read the documentation of your player first, how to achieve to set any other relation between album art and any other tag field, provided that this is possible ever, anyway if this is not possible, your trick should work.
QUOTE (RobG @ Jan 3 2010, 12:14)

... when I look at the info on my S9 it now says 'unknown' where the artist and title are but it says them correctly on my PC? It seems to have also hidden the artwork as it has dissapeared. I have changed back the changes and everything goes back to normal and I've also tried using both a space and a fullstop instead of the underscore between %artist% and %album% but neither make a difference? ...
I assume that you have to take another look into the documentation of your player.
Find there a statement about what Tag Format and what Character Encoding can be used by your player. Set Mp3tag to these values in the dialog Mp3tag/Tools/Options/Mpeg[Write].
DD.20100103.1550.CET