This answer explains how you can create your own custom error pages, using custom pages will help with the branding of your site.
This article applies to Linux Shared Hosting accounts.
How do I create my own error pages?
Open Notepad or a similar text editor
Copy and paste the following text into your new .htaccess file:
ErrorDocument 400 http://www.mydomain.co.uk/400.html
ErrorDocument 403 http://www.mydomain.co.uk/403.html
ErrorDocument 404 http://www.mydomain.co.uk/404.html
ErrorDocument 500 http://www.mydomain.co.uk/500.html
Replace "mydomain.co.uk" with your own domain name, then save the file with the file name ".htaccess"
Make sure that the file type is set to "All Files".
Click the "Save" button.
Tip:You will need to upload the error pages, e.g. 404.html
Upload the .htaccess file to your webspace.