Internal Error Message Adding User Who Has Another Account

editor1
Community Novice

I'm trying to add someone to my course in the "teacher" role. He told me he has another Free For Teacher account, but I want to add him to my course. When I try to enroll him I get an "internal error" message. I tried also adding him in the student role, but I got the same error message. To troubleshoot I added "myself" using some spare email addresses I have, no problem. So the issue is not adding users, but rather his email addresses. I'm assuming this problem is related to his other account, but I need him in this course. Does anyone have a suggestion for how to resolve this conflict?