Okay... this isn't really giving me anything to go on, here. Something is corrupt, but I don't know what. If it was DirectX or SlimDX, I'd expect a more sensible error. If the game executable itself was corrupt or if .NET was corrupt, this is more what I'd expect. My suggestion would be to reinstall the last official version of the game into this same folder (or if you are on Steam or Impulse, have it "verify the integrity of the files" or whatever the wording is when you right-click the game in their client programs). Assuming that it is the game that is corrupt, that should fix it, although you may need to temporarily rename your settings.dat to settings2.dat until you then upgrade back to the latest beta, then put that file back in place.
Also, one other thing that you could do is look under Control Panel in windows, then Administrative tools, then event viewer. Then look under the Application section and see what has any errors in there -- odds are, the AI War error is there, though what details it will have I don't know.
You didn't recently uninstall some version of .NET or anything, right? You might want to run a scan for viruses and spyware just to make sure nothing like that is after your stuff. Might not be a bad idea to run a scandisk, too, if it seems it is something system-wide -- bad sectors on a hard disk can cause this sort of thing.
You could also temporarily try renaming settings.dat to settings2.dat and then run it again to make sure that there's not something really crazy going on with that file (though the latest versions of the game should failover even if so, and should give a vastly better error eitehr way.).
And if none of the above works, then that would be when it comes time to uninstall and reinstall .NET 3.5 (and/or 2.0, if that is there) -- that's a last resort, and hopefully not what you will need, and that would be definite evidence of either spyware/virus or hardware problems.
Hope that helps!