When the file scanning is finished, avast! comes up with a number of files listed as "unable to scan", even though I have used a thorough scan. Should I be concerned?
Some files are permanently locked by the system or they are in password-protected archives. These files cannot be scanned. It is normal and you donīt have to be worried about that.
source: http://support.avast.com/index.php?_...tcategoryid=20

re: 2 anti-virus.

Some conflict with each other like Norton and Mcfee. IMO, no need for two, just make sure that the one you have is always updated.