As per experience before.
Whether it was SEP 11.x or 12.x, I have encountered that during the very first attempt to update the SEP Manager (after installation), I usually get an error where in the definitions are not updated.
The SEP Manager is connected thru a proxy server.
Initial troubleshooting done is downloading the JDB virus definitions (and the client definition for the server itself).
After uploading the JDB virus definitions to the SEP Manager, virus protection is updated.
And after trying to use LiveUpdate on the SEP Manager console, downloading was good already.
And good news is, it regularly updates itself; no download errors so far and it never misses connecting thru LiveUpdate.
Just sharing. I just hope my problem is not experienced also by others, especially on current version (and hopefully on the upcoming Beta).