Camera Raw stopped opening Canon 5d Mark II files

After working for a few weeks, Camera Raw has stopped opening Canon 5D Mark II files. Says it is not a readable file format but I know the files are not corrupt because they will open in the Canon utility.

Help appreciated.

I have already reloaded the latest version of Camera Raw from the updates.

What version of PS and RAW are you using?

Did you follow the instructions exactly for installing the latest (5.3) version of ACR? And did you remove any older versions of the ACR plug-in before adding the latest?