Deny usergroup access to a custom script

[WorldCraft]

Hello, I'm trying to deny access to a custom script for certain usergroup/s.

Even though I am specifying specific usergroup ID's, all usergroups are being denied access.

PHP Code:

require_once('./global.php');
if (!is_member_of($vbulletin->bbuserinfo, 19) OR !is_member_of($vbulletin->bbuserinfo, 20))
{
        print_no_permission();
} 

[nerbert]

if(! (a OR b)) => if(!a AND !b)

[Badshah93]

PHP Code:

require_once('./global.php');
if (is_member_of($vbulletin->userinfo, array(19,20)))
{
        print_no_permission();
}  

// This will deny access for usergroups with ugpid 19 & 20