Apple TV Mirroring Icon does not appear on a Mac Air
I have just purchased an Apple TV to mirror either my Macbook Pro or Mac Air to my TV. Both have the latest release Mountain Lion S/w updates. I get the icon in the status bar of the Pro and mirroring to the TV works fine but no icon on the Air. The Air is the latest 2012 model. I also have a similar problem on my iMac.
They are all connected via a wireless network. The Apple TV can see the Air's ITunes content so there is a connection between the Apple TV and the Air but no mirroring icon.
Any suggestions
MacBook Air, OS X Mountain Lion (10.8.2)