Lots of people are thinking there’s a problem with the Mac version of Photoshop Elements 10 as an external editor for programs like iPhoto, Aperture, or Lightroom. If you’re having this problem, 99% of the time, you haven’t really set Elements as your external editor at all, even if you thought you did.
In Elements 10 for Mac, the actual Editor application is hidden away in the main Elements 10 folder inside a folder called Support Files. Who would think to look in there for the program itself? But that’s where Adobe hid it, supposedly to make things easier for beginners, or so they say. What you see at the top level of the PSE 10 folder is actually an alias to the Welcome Screen.
So when choosing Elements 10 as an external editor here’s the file you really want:
If Elements is opening but no image appears when you send one over from the other program, that’s almost certainly your problem. Go back and change the chosen External Editor to the file where the arrow’s pointing in the illustration, and you should be all set.