I have also been having problems.
Dual booting Windows 7 64 bit on SSD and Windows 8 on regular SATA platter drive.
Was working ok then began getting constant freezes in Windows 7 but NOT in Windows 8.
Saw the messages about Avast ver 7 freezing people's computer and said " AHA ".
Yesterday morning I un-installed Avast and haven't had a freeze since.
My laptop also running Windows 7 64 bit and Avast does NOT freeze.
I suspect it is a combination of a Avast update, Windows version, and processor type.
This desktop has an I-7 processor the laptop has an old dual core processor.
The only combination that causes freezes is Windows 7, Avast, and the I-7 processor on my SSD.
With Avast and Windows 8 and the I-7 processor there is no freeze.
Many many people in the forums for my SSD drive Corsair Fore 3 have been fighting constant freezing also and Avast may also be their problem.
I just ran a virus scan using Avast ver 7 Internet Security on my Windows 8 installation and had it scan the Windows 7 SSD and it found two files that it couldn't scan because they were partially locked because another program was using part of them it said.
Very strange message, because NOTHING on the SSD drive should be being accessed because I booted into my Windows 8 drive.
The" busy " files were in Nvidia/GL Cache.
Scanning the Windows 8 disk with Avast it declares there are no infected files. No problems get reported.