Ensure they have Active, Staff, and Superuser checked for their account status.
NOTES:
Active status - should be automatically checked (for a newly created non-admin user).Active is not checked, then even though a user's account may exist on the system, they cannot login to it. This may be the case if an account has been disabled for some reason.Staff status - indicates that a user is at least an admin-user, which means they can access and execute operations on the Administrative page.Superuser status - indicates that a user is a superuser (and, by default, also an admin user), which means they can access and execute all Django admin pages and operations as well as all Administrative pages and operations.