Probably in reference to my comment:
This is probably where I stop and just ask BlackBox about it. Meanwhile, if you have a CD, or a CD install, use that as a base, and copy the new exe into that folder.
BlackBox was the one that packaged the updates. He would know more about those changes that are causing the incompatibility between this patch, and the usual multiplayer install.
As for that single player unit limit, keep in mind that an AI would be a second player. So if you're really playing single player, there can be no opponent, AI or otherwise. Hence there is absolutely no reason to build any combat units, other then to kill your own base. For that reason I was half tempted to leave the vehicle limit as it was, and just up the building limit. But then I figured someone would want to bulldoze the whole map or something, so maybe I should up the vehicle limit just a bit too. At any rate, I saw people trying to fill the map with buildings as more likely then filling the map with vehicles. Hence the disproportionate change.
The other game styles has both the vehicle and building limits doubled. Most of them, possibly all of them, allowed for more units than buildings. But of course those are the ones that allowed for combat.