I am having the same problem.
I have my 411j running 4.0 media server. It is connected to a Gigabit switch. The Gigabit switch connects the TV with the 411j, and to a wireless AP. The wireless AP connects to a wireless router, that connects to the internet. All my wireless devices connect to the wireless router directly, including a GalaxyS2 phone and an Xbox.
Initially it took me some time to set the system up in a way so that the wireless clients could reliably connect to the media server, but now once again I can't see the media server from the wireless clients, only intermittently.
Looking for all the help I can get.