I have got the same problem.
I did 3 things yesterday.
1. Changed old Kerio Firewall to Zone Alarm (reboot without problems).
2. Updated some programs (PotPlayer, uTorrent, Adobe Air)
3. Updated Avast to newest version.
It ended in endless loop of reboots.
Removing Avast (safe mode) cured system,
Fresh install and I got BSOD when avast wanted to do quick scan after installation.
After that the same loop of reboots.
Print screen from BlueScreenView:
http://i.imgur.com/OKjkfYJ.jpgBlueScreenView most of the times ID the ntoskrnl.exe as culprit, with fltmgr.sys ; aswSnx.sys ; aswMonFlt.sys as the rest of files "in the stack of the crash".
One time (while trying to scan after new installation) the suspected culprit was aswSnx.sys .
That is the second big problem I had with Avast in couple of months (Avast deleted important file and my father lost keyboard in Windows, I failed to restore it and had to reinstall windows), now I will probably try to look for a different Antivir solution.
PS. I am using Windows XP SP3