In the htaccess file at the root of your site, just make these changes:

In the htaccess file at the root of your site,  just make these changes:

ErrorDocument 400 /error.php?err=400

ErrorDocument 403 /error.php?err=403

ErrorDocument 404 /error.php?err=404

ErrorDocument 500 /error.php?err=500

into:

ErrorDocument 400 http://YourWebSite.com/error.php?err=400

ErrorDocument 403 http://YourWebSite.com/error.php?err=403

ErrorDocument 404 http://YourWebSite.com/error.php?err=404

ErrorDocument 500 http://YourWebSite.com/error.php?err=500

"http://YourWebSite.com" of course stands for the url of your website.