It is up now.
I don't know if this was a temporary thing at the time you tried to connect or something more sinister like a HOSTS file blocking avast.com, but that too should also block the forums.
What type of scan were you doing, Thorough, with archives, etc. ?
With it at 99% done, is the avast 'a' icon still rotating ?
What folder has it stopped in, last scanned file, reported, etc. and are there any large files, .avi files, etc. ?
What CPU% is being used in Task Manager for avast processes, they begin with asw or ash ?
I don't have any experience of the WHS version, but I wouldn't have though installing from there would have this kind of impact.