The only way I can get it to work, it would seem, is to disable Avast.
I don’t think this is a big deal, as I rarely run Activescan Pro on a computer that has working antivirus software, but still kind of strange and something that should be looked into.
Every virus can be identified, because it contains some unique signatures. Antiviral programs have their own database of that signatures. We call this database the "virus definition file". When an antiviral program scans a file for viruses, it compares all the signatures (of all viruses) in the database with the signatures in that file. If the signatures match (they are the same), the file is marked as infected. For an antivirus program, it is important to hide this database of signatures somehow - e.g. by encrypting it. Panda Antivirus does not encrypt its virus database - the signatures inside are clearly "visible" to other antiviral programs, so they detect this file as infected (but there is actually no virus inside - only the signatures are the same).