This sounds like you are using the Web Gateway for filtering. This is a separate product from VirusScan so any perceived upgrade problem is simply coincidence.
It sounds like the Web server is in a DMZ, perhaps the Web Gateway cannot access this resource which is why you are seeing it fail to connect to the server, or get a notification (probably says "Could not connect"). This would need to be investigated by your firewall team to make sure the Web Gateway has proper access to that destination.
Thank you for your reply, Jon! I will pass it on to the folks supporting the firewall and see what they can find.