I had a "similar" situation occur when I modified some network settings and
although the overall connectivity of my server was fine, I could not for the life
of me, get the updates to work again.
Ended up I had to go into the Nod32 advanced settings console (F5) and just
change some "stuck" proxy server settings (that didn't revert from the
windows network changes)...
It's been a while now, but I believe they were located within "Update --> then
Advanced Update Setup button " and/or "Miscellaneous --> Proxy Server".
Worth a look...