atapi.sys error - blue screen after update or scan

Have 2 identical Dell D610’s, one runs Avast 6 free just great, the other one bsod’s as soon as I install Avast.
No one has any answer. I have looked at everything side by side on both of them. Debugging tools say atapi.sys problem. Really want to find out why?

I seem to be having the exact same problem. And with Avast disabled I have no more problems. Here is my post on this: http://forum.avast.com/index.php?topic=73795.msg615740#msg615740