Normally the option to include external URL (e.g absolute, shape http://site.tld/url)
the function include is disabled by default in php5 versions, to activate this option on your server put these two lines in your php.ini
allow_url_include = 1
allow_url_fopen = 1
For more information, see: http://www.php.net/
... # ini.allow-url-fopen
Note that:it can be very dangerous to activate the option allow_url_include.
Indeed it may, in some cases, pose serious security vulnerabilities.