I just tried it on the 737-200 American Airlines livery and it worked fine.

This is what my aircraft.cfg looks like now:

[fltsim.0]
title=CS 737-200 Captain Paint0
sim=csx732
model=
panel=
sound=
texture=aa
kb_checklists=
kb_reference=
atc_id=N754UA
atc_heavy=0
atc_airline=American Airlines
atc_flight_number=732
ui_manufacturer=Boeing
ui_type=737-200
ui_variation=American Airlines
ui_typerole=Commercial Airliner
ui_createdby=Captain Sim
description=737 Captain (737-200) v1.0\n(c) 2012 Captain Sim www.captainsim.com

[fltsim.1]
title=CS 737-200 Captain Paint1
sim=csx732
model=200
panel=
sound=
texture=af
kb_checklists=
kb_reference=
atc_id=F-GBYA
atc_heavy=0
atc_airline=Air France
atc_flight_number=732
ui_manufacturer=Boeing
ui_type=737-200
ui_variation=Air France
ui_typerole=Commercial Airliner
ui_createdby=Captain Sim
description=737 Captain (737-200) v1.0\n(c) 2012 Captain Sim www.captainsim.com

And this is what is inside the model.cfg in CS_B737-200\model folder:

[models]
normal=x732
interior=x737_interior_fdo

No need for me to edit any files. It works fine for me. Not sure why yours is not working correctly. :-/

Mark