Thanks Old Toad
This resolved this issue. But, I am surprised. Aperture would open PSE without problems. Also, when I looked under <home>/Applications/PSE10/PSE10 the latter was what I had always selected previously. I showed that it was last modified in 2012. I had always selected this level for my editor (one level up from your recommendation) and it has worked in Aperture and used to work in iPhoto.
I checked <home>/Applications/PSE10/PSE10/support files/PSE.app and noted that it had been modified yesterday when I was having trouble. So, it was launched, as I mentioned, but no photo for image editing was appearing.
Today, I went back into iPhoto and reselected PSE as you recommended and it worked! An image now appears.
I thought that was odd.
But thanks for getting me up and running again!