You've been assigned an action, but when you try to click on the action to see what it is or close it out, you receive a 404 page not found error.

This 404 error occurs when you are assigned a task related to a record within a location that you do not have access too. With the access blocked, you see a page-not-found error. If you believe you should have access to this action, contact your system administrator to enable your rights in that location.