Metal Gear Solid: Peace Walker is no longer available on the Xbox 360 Games on Demand service.
The HD port of Peace Walker, originally released on PSP, was previously available for $19.99 but has been pulled from the service.
Konami hasn't provided an official statement on the circumstances, though players have previously reported the game suffers from random freezing and console lock ups, so that's one possible reason for its disappearance.
Peace Walker is still listed on the Xbox.com database, suggesting its removal may be temporary.
We've sent Konami an e-mail and will update you with more information soon.
Peace Walker was first released in 2010 exclusively for the PSP. It was given a lick of HD paint and re-released earlier this in the Metal Gear Solid HD Collection.
The first Metal Gear Solid: Ground Zeroes gameplay video was released over the weekend.