D2L prevents students from emailing the Course Classlist while a quiz attempt is in progress in an effort to minimize cheating. However, this security feature carries over to the Instructor role. 

If you receive an "Error: Not Authorized" message when attempting to email your Classlist, please check to ensure you do not have any quiz attempts in progress.

You can view any quiz attempts in progress by opening the "Update Alerts" menu next to your name.

Return to any in progess quiz attempts by clicking on the link in the alerts menu and "Submit" the preview attempts before attempting to email your Classlist again.