Missing Audio and Lost Project

• I loaded a project I have been working on and saving periodically, both to my internal D drive and an external Passport drive.
• When I tried to load it yesterday, I got a Missing Audio message and a long list of files Sonar could not find.
• Naturally, I tried more than once and even rebooted and retried.
• I had to revert to an older version of the project which means a lot of lost work.
• There is no way I would knowingly or unknowingly delete a folder or set of files—and Sonar found the folder—just not the files.

 
This is yet another one of those cases in which something mysterious happens in between saving a project and loading it the next time.
Ideas?

Hey, Conley, thanks.  So, I don't recall what the message looked like, but if I can find the files, will Sonar let me browse to them and open the project normally?

When I am working on a project, I hit the Save button on the V-Studio 700.  Then I do a Save As to the other drive.  So, one time the Save button goes to the internal drive and the Save As goes to the external.  The next time I hit the Save button it defaults to the external (since that was the last location) and the Save As goes to the internal.
 
I seldom do more than 15-20 minutes of work without saving, but that is variable.  If I am mostly listening and making small changes, I might wait an hour between saves (but never longer).  If I am writing parts or doing major edits, I save every few minutes.
 
When I re-open a project, I open the version listed first in the File drop down unless Sonar has crashed during the last session which screws up the file list.  If it has crashed, look on both drives for the one with the most recent timestamp.
 
I have been saving projects like this ever since I have been on X1.