One of our users is receiving the following error message when attempting to send an email from a case he is the owner of. Our other users are not encountering this issue. After reviewing his profile and permissions, I've not found anything missing. His profile seems to have access to everything necessary for sending an email from a case. Debugging around his user while reproducing the error didn't turn up anything either. I've included a screenshot of the debug logs from recreating the error as his user further below.
Does anyone know why a user would be encountering this error message while sending an email from a case they own?