Canon EOS 6D Instruction Manual page 366

Troubleshooting Guide
The LCD monitor does not display a clear image.
If the LCD monitor is dirty, use a soft cloth to clean it.
In low or high temperatures, the LCD monitor display may seem
slow or may look black. It will return to normal at room
temperature.
[Eye-Fi settings] does not appear.
[Eye-Fi settings] will appear only when an Eye-Fi card is inserted
in the camera. If the Eye-Fi card has a write-protect switch set to
the LOCK position, you will not be able to check the card's
connection status or disable Eye-Fi card transmission (p.339).
Playback Problems
Part of the image blinks in black.
[33: Highlight alert] is set to [Enable] (p.240).
A red box is displayed on the image.
[33: AF point disp.] is set to [Enable] (p.240).
The image cannot be erased.
If the image is protected, it cannot be erased (p.265).
The movie cannot be played back.
Movies edited with a computer using the provided ImageBrowser
EX (p.393) or other software cannot be played back with the
camera. However, video snapshot albums edited with EOS Video
Snapshot Task (p.232) can be played on the camera.
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