Open Externally not working

I am comparing two folders deep in C:\Users\alan\AppData\Roaming\Mozilla\Firefox\Profiles When I try to view a png file externally by right clicking and picking 'open externally' meld tosses up an error. Attached. There are no spaces in the paths. I'm launching this from the command line in cmd.exe Even if I do it via meld in the gui and pick the two folders for a dir match, it still errors.

using meld 3.18.3 Windows 10 fully updated 64bit.

I have the two "chrome" folders, one in the current directory "profiles" and the 2nd in 'profiles\firefox.default". The command line is meld firefox.default\chrome chrome. Meld of course adds the full paths. I move the two files to my Downloads folder as two different names in an attempt to make a shorter path, but that didn't help.

I upgraded 3.20.4, latest of website, and similar thing happens. Different screwy paths though in the error.