The microSD card may be faulty.
One good thing to try is while the microSD card is inserted into the phone try copying a picture from the computer to the phone's microSD card.
Plug in the phone to the computer, allow computer connection. Then on your computer navigate to card (not phone).
Then go to DCIM folder, then camera, copy a picture to there and see if it copies fine.
When it is done copying try accessing the same picture via the phone.
If you can't access the picture that was copied from computer to the phone's memory card via the phone then I would say the microSD card may be faulty.