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... 

Jason