I know it’s been years since this question was asked, but since I had the same problem I thought I would give a little insight to anyone else who may have this issue. One of the pins/contacts in my SD slot on my 6d was somehow pushed back and bent in half away from the SD card, and didn’t make contact with the card. I tried using a small nail to bend it back out but ended up breaking the pin. I disassembled the camera to where I could see the SD card slot was micro-soldered onto the mainboard. It has extremely tight tolerances and requires a micro-soldering station to de-solder it and attach a replacement. I found the part on ebay for ~$12 and when it came in I took the main board and the new sd card slot to a local shop that specializes in micro-soldering. They quoted me a little under $100 and had it completed within a week. I had also gotten a quote from a shop that specializes in micro-soldering on DSLRs, they quoted me $150-160 including the cost of the part. I would HIGHLY recommend paying a...