As I posted in another thread, I updated the Avast Free Program to Version 5.1.864 and had a problem with the Avast File Shield. When engaged this Shield blocked Explorer from accessing my Windows XP Pro SP3 32-bit Recycle Bin in all Accounts on my WinBook Laptop. When Explorer was blocked, Windows froze and had to be restarted with a hardware reset.
I removed Avast completely, and installed Avast 5.1.874 beta and the problem went away.
Since updating the program through the interface to 5.1.884, I can report that there have been no further issues. This is the version currently being offered through the Avast Interface.
Thanks for the swift action on this problematic update.