My OS is Win XP SP3. I have been working on this problem for about 2 weeks - luckily I have good secondary malware protection.
I have been a more-than-satisfied user of Avast! Free for a number of years, but when I ran into trouble with installing v6, I assumed that remains of earlier versions were causing the trouble. I therefore ran aswClear.exe several times in Safe Mode checking for remaining items on each occasion, but that did not clear out all the files and registry entries. This I have now accomplished, but the problem remains, namely.
As some others have commented, on-line registration says that it can’t find the file, and off-line registration provides an email with an incorrect licence code and it only refers to versions 4 and 5. Could this be the problem? I attach a copy of most of the email.
avast! 6.x: Inserting the license key into avast! Free Antivirus
On-line registration
Off-line registration
On-line registration is very simple and it's the preferred method for all users of avast Free Antivirus 6.x installed on a computer with standard Internet connectivity. To perform on-line registration follow these steps:
Please remove the registration file as it provides information on the registration format that could prove useful. Even if you were able to use it, if it were harvested it is likely to be blocked.
Did you actually try the on-line registration through the avastUI ?
I have recently done that and had no problems in doing so.