I had a similar error with my K-3 and a Transcend 64Gb card yesterday. I shot a bunch of photos, downloaded them onto my computer via a card reader, all went well. Then I was just previewing the images on the card, in the computer, when all of a sudden I got a fatal error message (Windows 8.1) requiring a reboot of the computer. When I put that card back in the K-3 it said "can not write to card" so I figured it needed formatted again - did so, in the K-3, same error. On a lark I put the card in a Canon 70D, formatted it in camera, and it worked fine. Transferred it to the K-3 and voila! It worked absolutely fine.
Seems to me the issue is in Pentax/Ricoh's implementation of formatting.
*update*
Just did the same thing, uploaded images to a computer (this time a Chromebook) and when I put the card back in the K-3, it said "Card is not formatted".
*update 2*
Read a
post on DPReview that helped. Put the card back in the computer, did a "eject" on the card, and now the K-3 recognizes it. How weird.