global_start Hook: Include External PHP File

[epic1]

In the middle of a vBulletin 3.08 -> vBulletin 3.6 upgrade.

I made this plugin for global_start:

ob_start(); 
include('C:/Inetpub/vhosts/fullthrottlev6.com/httpdocs/phpadsnew/banners/banners.php'); 
$BannerCode = ob_get_contents(); 
ob_end_clean();

And I call $BannerCode in my header. Nothing is printed. The plugin is active. Any pointers?
That's the exact path on my server, still no luck!