I sent my D750 in for warranty repair because the auto focus stopped working. When I got it back it refused to format the 16 GB Transcend memory cards I have been using since I bought the camera. They worked fine before and still work on my D7100. They are not locked. A 32 GB SCT card works no problem.
It looks like the firmware was "upgraded" in a way that bricks a lot of my memory cards. Weird.
Anybody know what's going on?