I am also encountering this error. Grayed out vehicles and all. In order to continue my game, I decommissioned my dropship and purchased a new one, now playing without the tank. I've played a ground mission since then with no problem, but I will definitely try to get in a couple more and report if I get another crash.
Edit #1
So I've played quite a few more ground missions. The overwhelming majority have turned out ok, and I was beginning to think the problem was dealt with. The last game however, the start of game crash occurred again, just as it had with the tank. When I reloaded the game and dispatched the dropship to the same mission again, the game played normally, without the crash.
