Can't export via shortcut

For some reason, suddenly I can’t export using the key command. I get this:

…but it certainly is not open anywhere else. And furthermore, I can successfully export it using the Export button.

It seems to be only this file (attached).
PS 23_half sheet.dorico (1.2 MB)

I am assuming that you had assigned a key command to either Key Commands > Print > Export All Layouts as PDF or Key Commands > Print > Export Current Layout as PDF.
To test, I assigned key commands to both of those and then used them. Both worked without a problem. I made sure that the key combinations I assigned had not already been used for any other shortcuts (which might override depending on context, as per warning messages I have received in the past).
Apart from the standard suggestions of quitting then relaunching Dorico and restarting the computer, all that comes to mind is that the file might have previously been saved to a folder which no longer exists or to an external storage device which was not connected when you tried to save this time. My thinking is that the “save” pathway might have been “remembered” in the file, and an error resulted when the location could not be found.