MacBook Air home sharing problem

I connected my iMac to a new Mac Air via iTunes home sharing. Authorisation was successful and the iTunes library was available on the Air. However, as soon as I start to play content on the Air, home sharing quits after a minute or two (it never gets through one song) and the Air tells me no content is available. The iMac continues to show that home sharing is turned on. After quitting and restarting iTunes on both machines, it eventually comes back, but with the same result as before. Firewall on the Air is turned off. Am I missing something in the setup?

Nick