I have an AirPort Express set up as a client in my existing wireless network just for AirTunes purposes. It works well for about three minutes and then it disappears from all my devices (two Macbook Pro's, an iPad and two iPhones). In my router, it is still listed in the client log with an ip address, I can still ping to it from the terminal and the light on the Express is still green. So in theory it should work. But it disappears from view completely, even from the AirPort Utility. The only remedy is to pull it out of the wall socket and put it back in, which recycles the problem (3-4 minutes online, then offline). I suspect the Express itself is not broken, since when I connect it to the network of a friend it continues to work as normal. Only in my network it seems to cut off in said timespan. To be clear, this is a 2010 model Express (the one that plugs directly into the wall) with firmware 7.6.1. On a side note, my Apple TV (which is another AirPlay device) stays in my network at all times, and I can access it at all times from any device. Any ideas?