I followed the instructions: used the uninstall utility in safe mode making sure it was aimed at the c:\program files\alwil software\avast4 folder, rebooted, installed avast 5 and rebooted. I now have the avast 5 icon spinning in my task tray and the status page shows resident protection and definitions auto updates are on. For some reason Virus Definitions Version has an orange exclamation point, but when I manually updated it said my definitions were current and the orange exclamation point remains. This is a new GUI I have to learn my way around, but so far it look much simpler than 4.8.
I didn't have any problems w/ the installation. I had some trouble downloading the license file. The first email listed an attachment but nothing showed up to download when I opened the email. A request to support by replying to the first email got me a second w/ a downloadable attachment. I found the instructions on when to doubleclick the license file a bit unclear, but on installation there was a page w/ several options - one being license file w/ a browse button so I could go to the downloaded license.avast file and select it. Easy. The subscription license status page shows I'm good.
I really should have remembered to upload the file IDed as a trojan to jobber to try and verify that it was malicious and not a false positive. I don't know why my avast 4.8 suddenly ceased working - the file reported as a bad image was aswCmnOS.dll and it seemed necessary for both the GUI and the command interface avast - as well as repair and uninstall via Add/Remove. It may just have been a Windows XP thing - critical files going bad w/ no warning and no known reason. A simple reinstallation replacing aswCmnOS.dll may have solved the problem - but no point w/ avast 5 available.
I know viruses target AVs so maybe it was a trojan and it targeted aswCmnOS.dll? A quick scan w/ avast 5 shows no current infection.
Thanks for the quick help.