I get this after replacing the export_descr_unit.txt with either of the mp versions:

"Script error in EB/data/export_descr_unit.txt, at line 1349, column 23.
Could not find soldier battle model for unit type 'Arabian infantry redsea axemen'."

...and a ctd. This only happens with my brother's computer, and comes when loading the menu. With mine it works like a charm (except for the closing error message).

Also what's the difference between the _custommp.txt and _mpcustom.txt?