I think the title says it all, and I can not remember what I change in the .cfg file. I know its here somewhere:

[fltsim.0]
title=C-5A USAF9007 (Gray & White)
sim=C-5A
model=
panel=
sound=
texture=1
kb_checklists=
//ui_manufacturer=ŒR—pƒWƒFƒbƒg—A‘—‹@
//ui_type=Lockheed C-5A Galaxy
ui_manufacturer=Lockheed
ui_type=C-5A Galaxy
ui_variation=USAF 9007 (Gray & White)
description=This is a heavy logistics military transport aircraft designed to provide world-wide massive strategic airlift. \nThe CONUS based fleet can provide delivery of palletized, oversized and outsized cargo, as well as passengers or combat-ready troops, anywhere in the world on short notice. \nThis enormous aircraft, first known as the CX-HLS (Cargo Experimental-Heavy Logistics System) transport, was required to carry a payload of 125,000 pounds (56,700kg) over a distance of 8,000 miles (12,875km), or twice that load over a shorter distance. \n\nby Kazunori Ito\n    KzIT16643VT@aol.com\n

[fltsim.1]
title=C-5A USAF70039 (Gray)
sim=C-5A
model=
panel=
sound=
texture=2
kb_checklists=
//ui_manufacturer=ŒR—pƒWƒFƒbƒg—A‘—‹@
//ui_type=Lockheed C-5A Galaxy
ui_manufacturer=Lockheed
ui_type=C-5A Galaxy
ui_variation=USAF 70039 (Gray)
description=This is a heavy logistics military transport aircraft designed to provide world-wide massive strategic airlift. \nThe CONUS based fleet can provide delivery of palletized, oversized and outsized cargo, as well as passengers or combat-ready troops, anywhere in the world on short notice. \nThis enormous aircraft, first known as the CX-HLS (Cargo Experimental-Heavy Logistics System) transport, was required to carry a payload of 125,000 pounds (56,700kg) over a distance of 8,000 miles (12,875km), or twice that load over a shorter distance. \n\nby Kazunori Ito\n    KzIT16643VT@aol.com\n

You need these 2 lines in the [General] section with proper entries. Specific to your problem, you must have an atc_type= valid entry or the sim uses 'experimental'.

[General]
atc_type=lockheed
atc_model=c5

Check here for valid FS2004 default atc type and model. FSX is essentially the same-
http://www.homepages.mcb.net/bones/Flight_Sim/data/FS_Aircraft_Codes.htm

Here is additional info on atc entries in the aircraft.cfg-
http://www.homepages.mcb.net/bones/Flight_Sim/tutorial/FST_CFG.htm

If you have updated your atc voicepack with EditVoicePack, model=Galaxy is also available, though it's spoken poorly in most voices..