LocalSettings.php when modify, get page cannot be displayed

[dorlow]

I'm trying to add a plugin (SQL2Wiki) to my corporate wiki site. One of the steps is to add

require_once("$IP/extensions/SQL2Wiki/SQL2Wiki.php");

to my LocalSettings.php file. As soon as I add it to the bottom of the site, the top of the site turns into the SQL2Wiki webpage. If I put in

require_once("/full/path/to/SQL2Wiki/SQL2Wiki.php");, it breaks the whole website and get a page cannot be displayed on every site.