As you may have found out already, the false detection was fixed with definition update 120828-2. Not long after you posted. If you haven't yet updated Avast, please do so.
See "Internet Banking False Positive Warning for Users with Avast! Antivirus"
My apologies for the late response.
Avast anti-virus is reporting that QuickBooks (QBW32.exe) is infected with the JS:Blacole-AV trojan horse when trying to open QuickBooks or open a company file.
This is a false positive and QuickBooks is not actually infected.