I have the same problem with my Samsung ATIV S. All of a sudden, I started experiencing access issues with the phone. One of these is the screenshot issue.
Here are all of them, I believe they are connected all together and have the same root cause.
1. Whenever I press WindowsKey+Turn off button to take a screenshot, the phone says Saving to Screenshots... and then Couldn't take screenshot. The screenshot does not get saved to Screenshots folder. If I check this same Screenshots folder via Windows Explorer, it shows the taken screenshot is there.
2. No camera app, including the built-in one, can save the taken photo. Whenever I start the camera and press the Camera button, the Camera app either disappears as if it crashed (and Start screen is shown) or the Photos app is shown instead of just taken photo. Checking the Camera roll section in the Photos app does not reveal the photo as if it wasn't taken. If I check this same Camera roll folder via Windows Explorer, it shows the taken image is there!
So the phone does take the photo and screenshots but can't read them! Why?
3. Most of the time Photos app fails on start. You tap photos, it shows Loading... and then the app closes and Start screen gets shown. The other time it shows Loading... then Resuming... then Loading... again and does that multiple times. Sometimes it starts well but shows only old photos and screenshots that were taken before I started experiencing issues with taking screenshots and starting system apps.
4. Often so the Phone storage app available in Settings doesn't start either and closes after showing Loading...
5. Music app fails to start every now and then. When it starts, it does not return to album view when you click Play on a song in an album. The app just freezes.
6. Finally, my System section in Settings|Phone storage|Phone now shows 4.29 GB (!) although it consumed 2.12 just before I started experiencing these strange issues.
It appears the issues arisen when I replaced my 32GB Transcend UHS-I QSDXC card with a 64 GB by µSDXC from Sandisk and attempted to synchronize photos via Zune application and both WinRT and Desktop versions of Windows Phone apps.
How do I fix this, any clue?