Black Ops 2 crash

In the mission Fallen Angel, the game crashes several times particularly when driving the SUV to leave town.
I lowered the settings to the minimum and still no help. I have updated drivers and have all required drivers installed.

Gpu Ati Radeon 4850
Windows 7 32bit
3.5 gB usable ram due to 32 bit (triple channel)

I finally was able to complete the mission but I still want to know what was wrong.