Is it temporary or a permanent problem?
It’s a permanent problem, since installation none of attempts to update was successful;
Does this occur with automatic updates or manual ones?
It happens with manual update, I haven’t used automatic updates yet
How did you set avast to update?
In fact I did nothing, I’ve just install it, typed the serial number and that’s all. Maybe it’s worth to mention that deb file which I downloaded from avast webpage didn’t want to install, so I created another deb using alien (from rmp archive) and that time it was successful.