Steps to reproduce:
1. Open the attached project(ScreenShotMR.zip)
2. Open the Assets/test.unity scene
3. Switch platform to Windows Store
4. Build for WSA Universal 10 SDK
5. Open Visual Studio solution
6. Deploy on local machine ( when Mixed Reality Portal is on and simulation/device is on)
7. Observe the Console:
Failed to capture screen shot
(Filename: C:\buildslave\unity\build\Modules/ScreenCapture/CaptureScreenshot.cpp Line: 413)

Expected result: Take a screenshot normally
Actual result: Error appers

Note:
In Editor works fine

Reproduced with: 5.6.3p1, 2017.2.0f3, 2017.2.0f3-MRTP, 2017.3.0b4

Favro card: https://favro.com/card/c564ede4ed3337f7b17986b6/Uni-29661