Bob that's really strange... have you tried reapiring avast! ? It may help, at least it's worth of trying.
I believe that Kamulko! just tried to help you Bob... he asked you can you check (actually, he said control) are all those file associations on your computer intact. Most likely he thinks that some graphic related program caused this behavior by changing associations, but I don't believe that's the case on your system right now...
It's something connected to how your system is "reading", interpreting avast! GUI at this point... maybe there is something in avast! code, that your system recognized as bug and it showed it to you... on other systems, everything works normal, but that doesn't mean that bug doesn't exist. Maybe some combination of settings on your computer just showed that something really is wrong. I'm sure it would be great if someone from Alwil pay attention to this issue, and maybe check on their side.
Thanks in advance Alwil !
Cheers !