Select the VIEW NETWORK STATUS TASKS under NETWORK and SHARING CENTER section
Choose wireless Network Connection or something similiar. If connected with ethernet then select it and press right button.
Click the properties button
Find Internet ''PROTOCOL VERSION 6(TCP/IPv6)'' anduncheck it, then click OK.
Restart your PC and try.
Reason For Problem
When u will use ipV6 , you have to setup your router and lan/wifi in ipv6 mode. Then bejour pass sound through ipv6 but when you use 2 mode ( ipv4 and ipv6 ) together benjour gets confuse some time it pass through in ipv6 and sometime ipv4 .if your router setup is ipv4 then, when banjour pass sound through ipv6 you will not see airplay button in itunes.
Hope it's clear to everyone .
If it works please click It Solved my problem or it helps me.