Error pages are served to Internet users when any one of a variety of errors occur, such as when a user enters an incorrect URL or is not authorized to access a specific directory in your web site. Companies often customize error pages to brand them with a specific corporate image and a link to their home page. You do not have to customize these pages - the error page is always available, whether customized or not. 

To create a custom error page for your account, please login to cPanel and click Error Pages, under Advanced. Select the domain or subdomain you want and click the page you want to edit. Insert your own custom page code (in HTML or SHTML). The changes will be applied after you click Save