Renaming files and folders works fine normally. You can run a chkdsk and see if there is any problems with the windows file system. Perhaps it will repair the file.
 
You said you looked to see if there were any shadow copies of the original file? as already mentioned you should make a habit of backing up anything you don't want to loose regularly. Having said that I probably would have just renamed the file like you did.
 
By the way do you have the autosave on in Sonar? If you you may be able to recover a previous version of the file.
 
Good luck.

It all depends on where and how you renamed it. If you used Windows Explorer to rename it all you need do is name it the same as it was before. If you did it right and used Sonar to rename it I have no answer for you.

Oh I missed that detail, I assumed he did a save as! Oh Oh, I would think renaming the CWP icon would be a bad deal. Sonar spooks me so much I'm even afraid to move stuff around once it's working. But I use folders for each song and re naming the folder is no big deal, but the icon is not something I'd mess with. So OP has done 2 things wrong here. The audio data should be unscathed but not sure what happens to midi when you corrupt a CWP icon file. 

I changed the folder name and the cwp file name to reflect the new title. 
 
 I tried renaming it back to what it was, but the same problem.

Cactus Music
I changed the folder name and the cwp file name to reflect the new title. 
 
 I tried renaming it back to what it was, but the same problem.

He may not be renaming it right. He will have to use Explorer to name it as it was as well as the folder. I do know this that Sonar will prompt for missing audio if the project knows it is missing. By going outside Sonar and not using Save As that project may be trashed.  

Did you also re-name your back-up(s) and did the same thing happen?

He's sleeping on it right now! Down under! 
 
1:14 AM
Saturday, May 3, 2014 (EST)
Time in Canberra ACT, Australia

Hey guys!
 
Haha!  So wonderful to hear from you all!
 
I ended up reimporting everything into a new session and rerecording all the midi parts.  Took me about 1/2 a day, so not as long as I thought.  
 
I didn't know that trick regarding time stamps, so that's great to know, especially when importing sessions from other studios that use ProTools (always a beef for me: wish it was easier to transfer).  I'll look into that.
 
For what it's worth, I do back everything up, especially for clients (this particular project was a personal one), but I hadn't got around to backing up yet, as I've only been working on it for the last 3 days.  I tend to do backups maybe once a week.  In all my years of recording professionally (about 12 years now), I've never lost a clients files; I'm pretty good like that.
 
Also, I actually changed the name of the cwp file and folder in Windows Explorer.  I've done it before without a problem; this time there was a problem, so won't be playing Russian Roulette anytime again soon and will use 'save as' next time!  
 
Also, all the audio files were still in the audio folder.  When I opened the session up, it didn't try to look for anything; it was literally an empty shell.  It was opening unmaximised and there wasn't even a master bus (or any bus) there anymore.  It was a ghost town!  
 
Really appreciate you all chiming in: what a great community.  I will do my best to touch base here and maybe help one of you out one day!  
 
warm regards,
 
Adam

When you re-name, the CWP file, you need to do a "save as" in Sonar. If you just change the name of the folder and CWP file extension, sonar doesn't know you did it.

Yep: I've used 'save as' in the past, but I didn't want it to create a new folder and reimport all the wave files.  I just wanted it to be labelled differently for my archives.  Shocked that the cwp file was corrupted by this.  Anyway, lesson learnt; I won't try and take that 'shortcut' again!  :)