> the first time I used xcc theme writer it worked great! However ever since I added my first mp3 to ra2, when I try to add any more it says the themes were written but when I start the game ALL in game text starts with MISSING:GUI
> and the game encounters an internal error while loading.This can only be fixed by reinstalling the game. Can anybody tell me if this is a bug in the theme writer program or a work around for this

It can be solved much easier by deleting ra2*.csf in your RA2 dir.

Is this about RA2 or YR?
Is the CSF file read-only?