Horrible graphical corruption and artifact MID game.

[Kudos]

I've played untill 1170AD and now all of a sudden I get serious graphical corruption. Sheets of graphic crap pollute the screen, artifacts show up in the water, lines come from everywhere and sometimes everything blacks out.

It ran fine untill this point and I've tried restart, alt-tabbing etc..

HOW the hell could they have missed something like this? (it happens consistently enough).

Specs:
P4 HT 3ghz
1 gig ram
6600gt