This is no false positive, and has anything to do with any kind of malware. If you read carefully the logs, you can see that the Avast Update program itself was the one causing the messages. The update program fails to write the registry. I have started another thread about this behaviour before this one was started (not that this matters), and still I'm waiting for an answer other than "don't worry about it, it's *probably* nothing". Well, is it "nothing" or not?
If anyone would like to take a look (even though till now they didn't answer either, as in this thread):
http://forum.avast.com/index.php?topic=35603.0 Let's hope the support team and the devs will take care of this soon, as they usually have done before. Thank you.