Obj file will not export (Blender 2.62)

Actually I do this several times a week since some years, export a obj with polygroups.
I added the blend file with the pant, the settings I want and the report that popsup.
Hopefully someone knows why this happens
In every version of Blender (5 on my HD this happens, only not with the 2.49b version)



Pant export test.blend (735 KB)