CS6/ACR 7.x not recognizing Canon 5d Mark 3 files previously edited in same version. Help?

Question

Why are my previously edited canon 5d mark 3 raw xmp files no longer recognized and all sliders set to zero? I can see the xmp files associated with the raw file in their folder. The files were originally edited in CS6/ACR 7.x -in July 2012 - and recently re-opened in the same CS6/ACR 7.x.
The canon 5d mark 2 files from the same time/event are showing up fine. I have updated everything, but both before and after the update, same issue with the Mark 3 files.
On a side note:
We have found that opening mark 2 files (that were originally edited in CS4 / ACR 5.7) in CS 6 / ACR 7.x and making any changes such as color coding causes all previous xmp information being zero'd out in the mark 2 xmp file. Not sure if this is a symptom of the same problem? Except the difference here is the Mark 3 files have never been touched outside of version CS6/ACR7.x - however the folder which holds both mark 2 & mark 3 files from the same event has been opened in the CS4 / ACR 5.7 window but without touching the files. By opening the folder in CS4 I can see that the Mark 3 files aren't reading and then know this event was originally edited in CS6/ACR 7.x
Specifics:
PS CS6 13.0.4 x64
Mac OSX 10.6.8
Canon 5d Mark 3 Raw files
This is the first time in these circumsances that this issue has presented itself.
Any insight would be much appreciated
Thank you!

Answer 1

First check to make sure your view mode in ACR is set to Image Settings, not Camera Raw Defaults.  This is accessible as the top item or three in the menu that comes up when you click the little threelines-arrow icon at the right of the tabs title bar, for example to the right of the word Basic.
Otherwise, did you switch your Camera Raw settings location to be the central database instead of XMP files and/or are you on a different computer that might have a different metadata storage location?
Open up one of the XMP files in a text editor, perhaps one that hasn’t had a picture opened for it, recently, yet, and see if you see any non-zero settings.  Also take note of the last file creation time.  This will help determine if the XMP files, themselves, have been written with ACR defaults or if they are just being ignored.
Also, check the date and timestamps of a CR2 and XMP file that hasn’t been opened, recently, and see if the XMP date/time is before the CR2 date/time.  There has been a bug, not sure in LR or PS, where if the XMP file date is BEFORE the raw-file date, then the XMP is ignored so maybe that could be happening.  If it is a LR bug, then have the files been edited in LR, which might have ignored the XMP files and the rewritten things with the LR default settings?
If no explanation can be found on your side, can you zip up a raw and its corresponding XMP, preferably one that’s not been looked at, recently, then put them online somewhere like http://www.dropbox.com/ and reply with the public download link, so others can take a look?
What version of Camera Raw are you using?  ACXR 7.4 just came out this week.