I kept my old copy of M:TW and just installed it on my newer computer. I can run the campaign mode just fine, but any time I take personal command of a battle (instead of letting the computer automate the outcome), then the next time I hit Esc (so I can save), the game crashes. Anyone know what's going on?

I'm running Windows 7 64-bit, i5-2400 processor, NVIDIA GeForce GT 520 graphics.