If you a Netflix user you may have noticed a missing Play button in the Instant Queue screen. Judging from the thread on Microsoft Answers its effected a lot of people and while Microsoft are aware of the problem there is no fix yet.
Fortunately Josh Pollard over on DMZ has a workaround:
Fortunately my wife found a work-around! While the “Play” button may be missing in action from the screen, the “Play” button on the Media Center remote still works! Hopefully a real fix is coming soon, but in the mean time, just push the button on your remote.