Umbraco error: The current user doesn't have access to this application. Please contact the system administrator.

We were alerted to this error when editors tried inserting links or images using the toolbar for tinymce. This is the error the got:

It was only happening for user type "editor" and not the administrators.

The solution mentioned in this post http://forum.umbraco.org/yaf_postst4772_The-current-user-doesnt-have-access-to-this-application.aspx states that you only need the Content section selected for the user, but this was already selected for my user experiencing the error.

The solution for me was to select the Media section for the user as well.