I would advise him to reinstall the App entirely on his device and try again. (I know, I know - duh. "Have you rebooted the Computer?" kinda suggestion. But you haven't mentioned that this has been done yet, so I mention it just in case.)
If that doesn't work, Tweet at Niantic Support AND send an error report via the normal way. Niantic Support on Twitter is inconsistent, but they do sometimes answer tweets very quickly.