A ten year old design flaw in Adobe Photoshop
Like all badly-written error messages, it did not make any sense. I was not trying to open any file; I was trying to open Photoshop itself. I was sure that none of the Photoshop’s files were changed. (A look on the access date of the files confirmed this.) Moreover, I was sure that even if Photoshop was somehow automatically updated, the file system access permissions were not changed. (AccessEnum tool confirmed this.) So, what was the problem?
My vague memories of ten years ago told me that it had something to do with the Photoshop configuration files. So, the proper course of action was to back up and delete the configuration files, forcing Photoshop to load with default settings. Pressing CTRL + ALT + SHIFT key combination immediately after clicking on the Photoshop icon discards the configuration files, although I strongly suspect that it does nothing in the way of backing them up. So, I backed up and deleted
Adobe Photoshop CS3 Prefs.psp, stored in
Application Data folder in my user profile. Since I was using Windows XP, it was stored in:
C:\Documents and Settings\John\Application Data\Adobe\Adobe Photoshop CS3\Adobe Photoshop CS3 Settings
Sure enough, Photoshop started without problem.
After that, I went through reconfiguring Photoshop, tweaking everything that needed tweaking manually. And then, it clicked: A few days before, I had changed the Photoshop Scratch Disk path but I had forgotten to modify the file system permissions so that Photoshop, while running in my user account, could have access to the new path.