I have a first generation Airport Express which works flawlessly with iPad and iPhone. But when I try to select remote speakers from iTunes it deselects the tickbox as soon as I click on it. Usually osx restart helps, but it only lasts until I switch network or loose connectivity to wifi. Expressively inconvenient I have to say.
I’m not alone, but it doesn’t mean that there is a straightforward answer out there. For some reason Apple is truly hiding all of their known issues and doesn’t list that stuff out on some FAQ page.
After many rounds of searches I found a hint that it may be caused by IPv6, as 1st gen Airport Express doesn’t support it. Disabling it for wifi solved my problem.
There is no “app” for that in OS X 10.7 so you have to use Terminal:
networksetup -setv6off Wi-Fi
You use LAN? No problem:
networksetup -setv6off Ethernet
Names may be different on other OS X versions, so check them with:
networksetup -listallnetworkservices