Ok, your steps don't quite make sense so I'm going to assume you meant:
Download update to HC -> Tools -> Software Update -> Update Program -> Select the LM-4S-G ? Correct?
What software version is the HC-2b running? It needs to be running 2.26 or later to properly access the LM-4S-G. If it's not running 2.26 or later update the HC-2b first and then try updating the LM-4S-G. You can check the HC-2b version by going to the Adjust Settings page of the HC.
It is possible you may have a faulty module, we had a thread here earlier this year with someone getting "Product Not Recognized" when trying to update an LM-4S-G but I don't know if the user actually sent the module back and if it was actually faulty or not.
- Tim