Forum Use of undefined constant VB_RELATIVE_PATH
 

I'm just trying out a forum upgrade and have copied the index.php from my forum folder (/vbb) to my root folder and uncommented the following line as documented in that file;

PHP Code:
define(VB_RELATIVE_PATH, 'vbb');

However, when I browse to / I get the following message at the top of the screen;

Notice: Use of undefined constant VB_RELATIVE_PATH - assumed 'VB_RELATIVE_PATH' in ###\index.php on line 32

The page still loads fine and seems to work. Any ideas what is causing the message?