Someone else had this issue.
I'll do a search for the thread, but try this in the meantime:
1) move ANY custom maps/mods/skins that are in your MOH\Main folder to another folder outside of MOH. Once done playing, you can replace them. If that dosen't work. . .
2) You may want to reinstall MOH and Spearhead:
http://mohaa.xgshosting.com/joe/installguide.htm