I took a look at the site with and without Network Shield on. Network Shield gives the popup attached. Without it, I just get a message that the site is not currently available (I have Prevx SafeOnline also watching the site; no reaction). So could be:
a. An Avast! incorrect IP blacklist-Avast! check
b. An IP that has become malware related since the older OA version here used it-OA upgrade should fix that
c. Older OAUI.exe has been taken over, so check digital signature
d. Other virus, so run an Avast! boot time scan

There have been no reports of recent OA versions having this problem. Current version is 5.0.0.1067.