It's a shame that it's not working for you - but if you have followed the instructions above and you are running 4.0.14 (although it probably works on any 4.0.x), then I really don't know why it's not working without seeing your code.
This was the first mod I've posted, so to be honest I dont know if it works on anyone elses system. It works on mine, so in theory it should work with others too.
I'm not an expert, but in order to try to make it work you could try the following:
1. Some servers have a problem with the 'getenv' function, so in my modification of auth.php, change
$session_ip = getenv('REMOTE_ADDR');
$session_ip = $HTTP_SERVER_VARS['REMOTE_ADDR'];
Then upload the ammended file and see if the IP addresses appear in your Users Online page.
To be honest, I think it's generally accepted that it's better practice to use $HTTP_SERVER_VARS rather than getenv anyway
If anyone else has tried this mod... did it work?