Started WSUS service on new server. Had WSUS running on a 2003 server - no migration. I let the server sit for a while as it collected updates and computers. Tried to approve and install updates for the 2012 server. Since this was just built a few months ago, there were a lot of updates from the last few years. This is the first 2012 server in production for us. Found over 6000 updates but when I tried to install for server 2012 only, all show as updated failed to download. Tried an update for IE 11 for workstation, but updated failed to download. Not sure what I missed.
We have a proxy but everything else worked when it was running on windows server 2003 R2, including our AV program. The only thing that changed was the IP of the server, name of the server and the OS.