Sounds like the path to Aces High has been messed up in the registry. Have you ever done a 'Windows Restore'? That could cause this.
Did you let the game auto-update, or download the patch from the WEB page?
If you are patched from 2.02 Patch 4 to 2.03 Patch 0, then you do not want to use the patch on the WEB site. You either let the game auto-install the patch or grab the small 2.03 Patch 0 to 2.03 Patch 1 from the news forum where Pyro made the announcement.