I can reach that file no problem.
It's ADSL through a router, other machines on the network can update no problem.
I don't think the internet connection is the issue here.
I think something is breaking Avast!...
I've been having issues with this machine lately...
First google results were taking me to couponmountain, then I tried to use regedit, and the explorer restarts...
Does this sound like a Conficter variant to you?
I'm not sure what it is, and nothing can find it, I can't update Avast! to get that to scan... I'm out of ideas right now...
Any thoughts?