Photoshop CS 5 "Document was made in a newer version" work-around

I've just had a student struggling to open a photoshop file. The "error" that came up was something along the lines of:

Cannot open document as it was made in a newer version

This was not the case though, as the student had only ever used that computer to make the file. I checked his disk space of which he had 50MB free, and the photoshop file was 90MB. It could have been caused by a lack of disk space.

You could see OS X making a nice little preview of the file, and so I decided to try and open it using Preview (which does now open new PSD files). I opened perfectly in Preview and I selected "Save As" from Preview and saved it as another PSD file.

This opened without trouble in Photoshop, but I did notice it didn't have any layers. I did not ask the student if this was how he had made it, but I think it should have had layers. My conclusion is that Preview, upon saving, merges the layers. I'm also assuming that the PSD file was originally saved for "maximum compatibility" which saves a merged layer.

So, in ultimate conclusion, always "save with maximum compatibility" in Photoshop. This way you might have a better chance opening a "broken" file in Preview and saving it out of this.