It was definitely created on the same machine, same version (CS3) and was created just one week earlier. I was lucky to find that the rest of the files were ok.
I did try two freeware and shareware programs, but neither worked. One could recover some background layers, that were very basic, but the main image file was completely corrupted. I also tried opening it in other graphics programs but could not.
I finally went back and recreated the file. It is possible that I had a crash while saving, or around the time that I saved. I remember that my hard drive was pretty full and I can’t remember if I cleared things off before creating this file or after. Hopefully it will not happen again! I have never had this problem before.
Thanks!