Sure you don't want to hear it... But still, the answer is contact your hosting provider.
But before you do, let me tell you why you probably shouldn't do so in the first place:
If the PHP file you want to include is included over a url (that is with http://
in front of it) , you will be asking the webserver of example2.com to give you that file. The webserver will then run that file through PHP (thus already parsing that file) and give you the parsed HTML that the script produces. And you will end up including the parsed HTML in stead of the original contents of the PHP file you are trying to include.
If by any chance example.com and example2.com are hosted on the same machine, try including the desired file by using an absolute file path to that file. (eg include "/var/www/example2/yourPHPfile.php";
)