Photos: "An error occurred while preparing external edit."
Running Photos 5.0 on my MacBook Air (Retina, 13-inch, 2020) with MacOS 10.15.7 (Catalina)
I have been editing a number of photos with an external editor (Graphic Converter 9 (9.7.5) without any problems. Then things froze up and the laptop rebooted itself. Since then I've been unable to edit my photos with Graphic Converter (or any external editor as far as I can tell) - I get this:
(for searching purposes: "An error occurred while preparing external edit. Couldn't communicate with a helper application")
I rebooted my Mac several times, including in recovery mode to run Disk Utility > First Aid - no problems were found.
Looking for advice on how to fix this, as I was trying to get some edits done before Sunday (2020-11-29) for a slideshow...
MacBook Air 13″, macOS 10.15