I am having this issue too. The only times it comes up are when I try to log in to World of Warcraft.
It started about a week ago, and I went through a series of steps over a period of about 24 hours as outlined in a number of posts on the 'Net, including the ones on these forums.
This seemed to fix it, but this afternoon it came back and I am having exactly the same problem: when I log in to WoW, Avast reports a virus and WoW won't let me proceed. The most recent report refers to this:
C:\ProgramData\Blizzard Entertainment\Battle.net\Cache\TMP\D8747EC8DC071C8E69441DC9309F4CD6C52AAF3E2ED04AE2DBA2AC93F5DCF056A15E9A4495608A1E\[UPX]
Malware Name: Win32:Malware-gen
Malware Type: Virus/Worm
VPS Version: 101005-0, 05/10/2010
I have tried all the options and then re-logged in to WoW: nothing fixes the problem.
None of my checks are showing any problem: HiJackThis, S&D, MBAM, AdAware, Rooter, OTL, TFC. Only Avast seems to be having problems.
ADD: I see that there are many people having this problem. You REALLY need to fix this. I - and probably many others - are paying for Avast Pro, and we're all certainly paying for WoW subscriptions. We are not getting our money's worth for either. Will Avast be reimbursing us for lost time on WoW, and for ineffective virus scanning?
Mike Boardman