A few days ago I upgraded my PC with a new motherboard, CPU and 16GB RAM. I run Windows 7 Ultimate x64 with all available updates, including Service Pack 1.
I upgraded my PC mainly to speed up the panorama stitching application AutoPanoGiga (http://www.kolor.com) but I was horrified by how unstable it became on my new hardware. After A LOT of testing to narrow down the cause of the problem, I came to the conclusion that I only had this problem when Avast! Free Antivirus 6.0 was installed. After uninstalling Avast 6.0 the instability went away and after re-installing it the instability came back. So I uninstalled it again and went back to Avast! Free Antivirus 5.0 and hadn’t had any instability issues since.
I experienced the exact same problem on two different PCs running W7 SP1 x64 with 8 and 16GB RAM. A third PC running the same OS but with only 4GB RAM did not show these problems.
Here’s my thread over at Kolor’s forum with more details about the problem and what I did to come to this conclusion: http://www.autopano.net/forum/t11578-apg-2.5.0-x64,win7-sp1-access-violation-crashes-on-i7-2600k-16gb