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.