"Edit in Photoshop" not working after latest update

After the latest update to Lightroom and Photoshop I am no longer able to select "Edit in Photoshop" when I right-click on a photo in Lightroom. The option is present in the menu but 'greyed out' and I cannot select it. The same applies for the various related options (i.e. "Open as layers in Photoshop", etc.).

I tried uninstalling and reinstalling Lightroom but the problem persists.

I can manually select Photoshop as an external editor but Lightroom isn't recognising Photoshop in the usual way.

IS this a known issue? Any suggestions?