Using $GLOBALS in a function within a class

Code reference from the book by wrox: Professional PHP 4:

I am trying to get the statement

$this->msg_no = $GLOBALS["msg_no"];

to work within my function which resides in a class. My error statement is the following:

Notice: Undefined index: msg_no in C:Apache2htdocs_developmentwebmailwebmail2.php on line 46

The catch is that my server online works fine.

MY SETUP:
WORKSTATION SETUP: WAMP(win2k, apache 2.0.43, mysql, PHP 4.2.4 dev).

SERVER SETUP: FreeBSD, PHP 4.2.2


Question: Is this a linux specific statment? or is there a setting on my workstation that I need to fix?

That statement shouldn't be specific to any operating system.

Where is $msg_no or $GLOBALS["msg_no"]; ever set to begin with? Is is possible that it isn't set? Maybe you server setup has a lower level of error reporting, so you don't know that you are accessing an undefined index...