Please try this again, if you got 0xC0000005 error, we want to resolve this problem soon.
Edit setup.ini file in avast4/setup folder, add the following lines:
[BufferLog]
Enable=1
Limit=0
Run update again (it will probably fail), and send me files Setup.ini, SetupDbg.log, Setup.log and your license key (only the letters before dash separator) to my email (forejt@avast.com)