Support for the Canon EOS 6D first arrived in Camera Raw 7.3 - only Photoshop CS6+ is compatible with Raw 7.3
You have two choices
- Upgrade to CS6, or
- Download the free DNG converter from the Adobe website, convert all your Raw files to DNG and edit the DNGs in Photoshop CS5.1
You'd have to ask Adobe to be sure, but I doubt that they'll offer you anything for free now that you've waited this long after the release of Photoshop CS6. But definitely ask.
This page gives info on upgrades: