This has been a problem for me with kyro since it came out.
There doesnt seem to be a fix for it other than selecting Shift F3 which bumps frame rate up alot but looks crap.
When I first got this problem I spent alot of time trying to fix it without success. Herc site was a waste of time.
Its something to do with the way the card handles that type of lighting effect.
I quite often log off at sunset sunrise times.
GF3 cards will soon be coming down in price now GF4 is out, the kyro will then be in the bin:D