Qim, check the folder C:\ProgramData\Avast Software\Avast\log
Are there any files called unpXXXX (where XXXX is a random number) or *.mdmp there?
If so, send them to
http://www.mailonpix.com/images/0da0c5e21c19d4858c8994a82e79b7d0.gif
They may contain more information about the problem (maybe a link to this thread).
Vlk explains how to create a dump file here: http://forum.avast.com/index.php?topic=22636.msg187340#msg187340 and here: http://forum.avast.com/index.php?topic=23283.msg193594#msg193594 
To create the dump, download and run http://public.avast.com/~vlk/hangrep.exe . In the list of processes select it and use the Save button. This generates a file which you can either send to his email address vlk (at) avast.com (if it’s smaller than e.g. 1 MB, ZIPed), or upload to ftp://ftp.avast.com/incoming
The command-line version http://public.avast.com/~vlk/userdump.exe . The syntax is
userdump.exe <program_to_dump>.exe c:<report_name>.dmp
(producing dump file in the root of C:\ drive)
Please note that prior to taking it, you’ll have to temporarily disable avast self defense - otherwise, the program responsible for creation of the dump won’t be able to open the process.
If you’re facing full BSODs, please, go to folder \windows\minidump and send the newest (recent) .mdmp files for analysis.
There is also C:\Windows\Memory.dmp file.
Better if you can compress (zip), rename it with an unique name, them and add some information about the BSOD and the link for this thread. 
Upload it to this anonymous ftp server: ftp://ftp.avast.com/incoming/
To generate full dump instead of only kernel (or small dump), see http://www.msfn.org/board/creating-memory-dumps-t130005.html.