Hello there, @SallyB11 ...
If you are trying to enroll this student in a second course within your school's Canvas environment, have you tried enrolling that student via SIS ID or Login ID instead of via his/her e-mail address? If you are a Canvas administrator, you can find a user's SIS ID or Login ID by going to their user profile within Canvas. See the screenshot at the bottom under the section "View User Profile" of this Guide: How do I use the People page in an account? - Instructure Community (canvaslms.com). On that screenshot, look at the section labeled currently as #2 (Login Information). The SIS ID and Login ID would be listed there. If you are not a Canvas administrator at your school, you can speak to someone who is, and that person may be able to help you get the student enrolled in the course for you.
Hope this will help a bit, Sally. Let Community members know if you have any other questions about this...thanks!
