Troubleshooting Steps for the Access Denied Error in Canvas
Confirm it is not a browser issue by clearing cache and cookies: Clearing Browser Cache and Cookies, and make sure your browser is updated to the latest version: Web Browsers - Updating Your Browser to the Latest Version
After you confirmed it is not a browser issue then this error is caused by trying to access a Canvas site that you don't have access to. This may be a assignment that is not yet posted, a class you are not enrolled in, etc. You might want to try reaching out to your instructor or talking with other students to check if they are experiencing something similar.
If you run into further issues contact the DoIT Help Desk for further assistance: Get Help from DoIT