Help with iTunes/AirPlay: pausing when trying to stream music over AppleTV3

Question

I've found since I upgraded to Mountain Lion on my late 2009 white Unibody MacBook, Airplay does not work well.
iTunes sees the ATV, and the ATV sees my music library. But it pauses all the time. Sometimes before it even starts playing, and almost always a few seconds before the end of a track. Extremely annoying.
By "pauses" I don't mean stuttering or dropouts. I mean that the iTunes button literally goes from "play" to "pause" on my MacBook.
I assume it's a Mountain Lion/ATV3 problem, because AirPlay works just fine on this AppleTV from my fiancee's late-2007 MacBook running Lion (don't know if latest version), and also from both of our iPhone 4S's. Just not from my MacBook, which is of course the source we usually want to use, because it holds my music library including all of my digitized vinyl.
It doesn't matter if I initiate play in iTunes on the MacBook, or on the ATV3. (As I wrote, it sees my library just fine.)
Any ideas how to fix it?
Here's the complete setup:
Late 2009 MacBook (white unibody), 750GB HDD, 8GB RAM
OSX Mountain Lion 10.8.1
iTunes 10.6.3
<wireless>
Apple Time Capsule router (I assume it updates its firmware when Apple releases new ones, I don't know version though)
<wireless>
AppleTV3 with 5.0.2 (4250) software, connected via HDMI to an Anthem MRX 300 A/V receiver.

Answer 1

HI,
I see you "reset" but if you didn't reset network settings.. do that.
Tap Settings / General / Reset / Reset Network Settings.
Then restart your iPad.Press and hold the Sleep/Wake button until the red slider appears. Slide your finger across the slider to turn off iPad. To turn iPad back on, press and hold the Sleep/Wake until the Apple logo appears.
Carolyn