[noggin]

Pretty sure it's not cable as everything else is working ie all apps on shield and Apple TV as using same cable it's only prime, also I'm only on 1080p  

If you are 1080p then it's far less likely to be the cable. 

Have tried other cables and no charge 

Your previous post suggests it's linked to the new, experimental, semi-automatic frame rate sync functionality (where I believe you can tell the Shield TV to sample the playing video, work out its frame rate, and then alter the output refresh rate for optimum quality)  My guess is that the way nVidia are sampling the playing video causes the Amazon Prime App to think the video is being tampered with and triggers a copyright protection error.