The scanner is in use by application '(null)'

Until now I've always scanned through the Printers & Scanners part of options. It's far from great so now I want to try scanning through Preview. Now I get this error message: The scanner is in use by application '(null)'.

And I get it both from Preview as well as the stuff I used before.

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Is there a good way to fix this? I.e. without rebooting.


I encountered the same question on my MacBook Pro. I solved it by changing to another USB port; I didn't have to restart.