That message might indicate a problem with the internet connection, for example if you have a firewall or a similar security software that is blocking online access to the update server.
Try to turn off all firewall and similar security software and try again.
In any case, if you download and install the Stand-Alone Addon Manager, you don't even NEED the update, because the Stand-Alone Addon Manager always includes the same set of files that you were supposed to download online so, even if something in your system is blocking access to the update server, you have the latest files anyway.