However I would say that "Sorry, you do not have permission to access this feature. Please contact your administrator for assistance." Is not an error message

However I would say that "Sorry, you do not have permission to access this feature. Please contact your administrator for assistance." Is not an error message, in the sense that it is not displaying an error state of the application. It is informing the user that some feature they have somehow reached (maybe through a link sent by someone else?) is not available to them. The apologetical tone is not for a mistake that was made (there was no mistake made by the application in this case) but for the action of preventing them from accessing something that is available to others.