The Python Implementation used by Blender versions up to 2.49, had changed drastically at Blender 2.5..
(and probably again a few times)
If someone could take the Old X-Exporter and "re-code" it "exactly" under newer Python rules then the problem would be solved..
(and that someone ain't me)
The best now is to just work (using Legacy Saveing Option) between Blender 2.49 and Blender 2.X..
(not really a problem once you've done it for a hundred characters)