Recovering corrupt files -- everything appears to be fine

Question

Operating System: Mac Osx
Computer: Macbook Pro
Program: Adobe Photoshop CS5
I was using adobe photoshop today for painting purposes (not to alter images). I saved the file multiple times just to be safe, and spent about 5 hours or so on a project. I closed the file quite a few times as well and I was able to open it no problem. Upon the last save (which, according to the program, was successful) I decided to take a break from the computer. After saving, I exited the file and proceeded to shut down my mac. It went through its normal procedure of quitting whatever programs were open. For some reason or another, Photoshop wouldn't quit, stopping the shut down. I forced quit (mind you, the file I hadopen previously was already saved and exited out of) and my mac shut down.
A few hours later I booted up my computer to continue working on the project. I clicked on the file and phtoshop opened like normal, began to load the file, and stopped suddenly saying that "There was a problem reading layer data. Read composite data instead?" I clicked yes and got the message "Could not complete your request because the file is not compatible with this version of Photoshop."
I researched the topic on several sites and found the file to be considered corrupt. I downloaded two recovery softwares. The first worked at recovering some layers -- but all of them were ruined beyond use. The second failed to work.
I guess my question is, is there anything else I can do to more successfully recover the file?
I don't understand how it can randomly corrupt. My computer did not simply "poop out on me" or anything. It shut down, like normal. And a force quit never hurt any of my photoshop files in the past.
Also, looking at the "info" regarding the file, the number of bytes remains the same, the layers remain in tact, the file type remains the same, color space and color profiles remain the same, etc. So what exactly is corrupt?
Please help!
I understand if the file is lost. I just don't understand how.
Thanks,
Sam

Answer 1

It's a risk you take with force quitting that your files get corrupt. Often they're fine, sometimes they're not.
For this Time:
File recovery programs have mixed results... I've normally used them when someone accidentally deletes an important file, but don't know how well they'd work for a corrupted file. Typically I can't recover any corrupted files. But you can hope that your computer just got a little confused and try these things:
First, I'd restart in Safe Mode. Hold down the shift key while restarting your machine. This is supposed to take it back to the last working settings - hopefully the settings that were working to open your document.
Then I would try zapping the p-ram (probably a good idea anyway). Restart your computer and when you hear the 'bong' sound, hold down apple + option + p + r (yes, it takes some dexterity). This will help if it's a problem the Computer is having at Reading the file, which it could be, since you say that the file is the right size and seems to have all the right data.
I'd also run Applejack, which will clear the caches and reset file permissions. Whatever process in PS is trying to read the file may not be able to access all of its parts because the permissions got corrupted but nothing else. This is also a good idea to run anyway.
It's free from here: http://www.macupdate.com/app/mac/15667/applejack
To run it after installation, restart your computer holding down apple + s until it comes up with white text on a black screen. Type applejack and hit enter. Autopilot should be fine, so type a and enter. Let it do its work and then restart it by typing r.
Tips for Next Time:
Don't force quit. Let the program cancel the shut down instead, wait for it to quit, and Then shutdown. Usually it's still working on something. In this case it sounds like it was working to save your document. It'll finish working on it next time if it can, and therefore recover your files, but shutting down will stop and reset any processes (normally the point of restarting) and increases the risk of losing your files.
If you saved it, don't worry about recovering the file through the program. It doesn't need to be recovered. The program only thinks it does, because that's the last thing it remembers. (You didn't do this, but it produces similar errors.)