Canon EOS 6D Instruction Manual page 358

Troubleshooting Guide
Shooting-Related Problems
The lens cannot be attached.
The camera cannot be used with EF-S and EF-M lenses (p.39).
No images can be shot or recorded.
Make sure the card is properly inserted (p.31).
Slide the card's write-protect switch to the write/erase position
(p.31).
If the card is full, replace the card or delete unnecessary images to
make space (p.31, 267).
If you try to focus in the One-Shot AF mode while the focus
confirmation light <o> in the viewfinder blinks, a picture cannot
be taken. Press the shutter button halfway again to refocus
automatically, or focus manually (p.44, 97).
The card cannot be used.
If a card error message is displayed, see page 33 or 370.
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