Right, checked the files.
The file set causing the problem is the Large Slide out Compass.
The Menu_ini of the IO mod can't find the following files in your GWX install:
ZeigerKompass.tga
Richtung.tga
Glas1.tga
The normal location go these are : data/menu/gui/Layout/
Now, they are all included within the IO Mod and, more importantly, a default install of GWX 3.0 (that's 100%, I put them there). In this instance don't assume the IO mod is corrupt, it's more likely that your GWX file set is, umm, borked.
MD5 check the GWX files to ensure integrity.
Also, there were instructions floating around for the removal of the Larger Sliding compass. Have you made any other changes?