If you come across a situation where your MacBook, MacBook Air, iMac or whatever computer you’re using is not able to find your Apple TV or other AirPlay enabled device over a wifi connection. And you happen to be using a Cisco RV series wireless router/access point. I would suggest that you trying turning on the WMM feature on the wifi network.
I have not determined why but for some reason if the WMM option is disabled, AirPlay won’t work. This has been tested on a RV120W and a RV220W. I think it would be the same with RV180W.
Hope this helps someone out there one day!
UPDATE Oct 2013
Thanks to David Redekop we discovered one more setting that should be adjusted.
Under Wireless->Advanced Settings make sure that “Protection Mode” is set to None. And click the Save button.