That "Someone" is right when you replace the batteries the ECU sometimes needs to relearn the key again (Not immobiliser, just remote side)

You have the correct procedure as well turn key to position 2 and off four times within 3 seconds, this activates "Learn" mode, this is signalled by the LED illuminating continuously, this happens for 20 seconds in which time you have to press a button on the key this, this will flash the LED once is successful. When done leave it will quit after 20 seconds have elapsed anyway, alternatively turn ignition back on.

Martin