Thank you so much. There was too much stuff in [HKEY_CLASSES_ROOT\.exe]
It was like [HKEY_CLASSES_ROOT\.exe\shell\open\command] which had a value pointing to a user's tmp file.
Deleting that whole shell section took care of it.
I did find "%1" %* in a couple of places and changed it to "\"%1\" %*" as your example showed.
However that yielded access denied errors when I tried to open *anything*.
Fortunately I had the foresight to save that key before I made the change and got it back.
It didn't like the backslashes.