It would probably work if it were set up the way ACES instructed in the SDK. If you write to me directly at n4gix@comcast.net I can send you my "MiddleMan/ModelCommander Plug-n-Play" package, which when unzipped into the folder structure as shown set up per the SDK, will allow you to export without further problems...
Directory of C:\gmax\gamepacks
11/13/2005 02:36 PM <DIR> fs2002
11/16/2006 09:01 AM <DIR> fs2004
02/13/2006 09:27 AM <DIR> fs2004_scenery
11/12/2006 02:02 PM <DIR> FSX_GmaxGamePack
Directory of C:\gmax\gamepacks\fs2004
07/16/2007 01:38 PM <DIR> .
07/16/2007 01:38 PM <DIR> ..
12/27/2006 01:16 PM <DIR> docs
11/10/2003 04:08 PM 17,227 EULA.rtf
04/06/2005 05:19 PM <DIR> extras
11/24/2003 09:29 AM 1,332 FS2004.lnk
07/15/2007 02:21 PM 5,618 gmax.ini
04/24/2005 04:23 PM 25 msmooth.ini
11/17/2003 10:26 AM 126 plugin.ini
04/14/2007 06:50 PM <DIR> plugins
07/06/2006 10:32 AM <DIR> scenes
04/06/2005 05:19 PM <DIR> scripts
10/18/2005 11:25 PM <DIR> texture
04/06/2005 05:19 PM <DIR> tools
Directory of C:\gmax\gamepacks\fs2004\plugins
11/24/2003 09:29 AM 167,984 FSModelExp.dle
07/02/2002 12:45 PM 34,455 makem.exe
03/19/2003 01:29 PM 577,536 makemdl.exe
09/06/2001 02:01 PM 41,008 md3exp.dle
07/14/2007 07:52 PM 1,098 mdlcommander.log
05/10/2004 04:19 PM 1,024,000 MkMDL.exe
06/23/2007 04:42 PM 187,721 MkMDL.parts.xml
02/08/2007 02:27 PM 708 mman.sys
04/15/2004 12:03 AM 127 mmans.sys
06/17/2002 08:23 PM 1,230,336 msxml4.dll
06/17/2002 08:23 PM 44,544 msxml4a.dll
06/17/2002 08:23 PM 82,432 msxml4r.dll