How to: Add an Error Document
Click the Hosting Features menu item if it is not already open.
Click the Htaccess menu item.
Click the [ Error Documents ] link for the directory you’d like to manage..
In the “Error Code” column, select the error code from the dropdown list.
In the “Error Page” column, enter the path to your custom error document, relative to the web root. Alternatively, you can enter a fully-qualified URL to another page.
Click the ADD button.