I'm assuming you already checked if the include path (../config.php) is correct, so we're gonna try something. It was suggested to me by someone here a long time ago when I couldn't get includes to work, it could be the same problem here.
Create a php.ini file and put it in the same folder (I think it would also work in the main root folder).
In the file, write:
Code:
[php]
; Whether to allow the treatment of URLs (like http:// or ftp://) as files.
allow_url_fopen = On
; Whether to allow include/require to open URLs (like http:// or ftp://) as files.
allow_url_include = On