[WonderMonkey]

I had to change it a bit. When I implemented your code I would get the error message as soon as someone clicked on the "register" link to begin the process. I was able to look at the code and figure out enough to do the following"

In register.php

// This is the Registration Code
if ($action=="addmember") {
	if ($specialpassword!='XXX') {
    	eval("standarderror(\"".gettemplate("error_inviteonly")."\");");
    	exit;
  	}
}

Of course I may have implemented your code incorrectly to start with.

Thanks for pushing me most of the way!