Are you using a push or pull method for your clients to communicate with the manaement server?
Either way... Do you know what the default port numbers are for both the "server conection" updates and the "definitions"?
I believe they are ports 3389 and 8014
Have you tried, from the client that is experiencing problems:
telnet [server name] 3389
telnet [server name] 8014
There may be something blocking on the server side if you are using pull method or something blocking on the client for a push method.
Also, I did not read the linked article, so forgive me, but have you ensured that the "Liveupdate policy" is configured to use an internal server: "Use the default management server (recommended)" and this value was not changed?