Last week, Canon made their new firmware available for the 6D. This is a minor update, but still worth completing. According to the manufacturer it "Fixes a phenomenon in which some images cannot be transferred to mobile devices running the EOS Remote app."
Updating software is a quick process, but if you've never done it before, here's how:
First, check to see if there is new firmware for YOUR camera.
Canon models are here.
Nikon models are here.
---Then, follow the manufacturer instructions that typically accompany the firmware upon download. While the process below is specific to the Canon 6D, the setup is very similar for most cameras.
Just to be sure it all worked, go back to your firmware menu, and confirm that the version number has been updated.