This was published on Canon UK’s site:
This issue relates to customers who are using the Digital Photo Professional (DPP ver.3.11.10) RAW image processing software with the Canon EOS 5D Mark III digital camera.
We have identified an issue that prevents users of the Canon EOS 5D Mark III from processing their RAW format images when using Digital Photo Professional Version 3.11.10, the RAW image development software that is bundled with the EOS 5D Mark III.
We will shortly release an update for the Digital Photo Professional Version 3.11.10 for users to download which will address this issue. The update will be released on the website in mid-April.
To learn more about this issue check forums.