The ESN was missing from our 6400 series LED telly but we could find no way to add it.
PLaced a call via email and got a reply within 24 hours. What's more it worked. Not sure why Samsung asked for the different network, but I did it as suggested.
To see if the esn is missing go into menu>support>contact Samsung, scroll down to the second page.
If the ESN is missing, Netflix is unable to function. The Netflix ESN can be restored by following these steps:
1. The latest software needs to be installed on the TV
2. Perform a factory reset. To do this, follow these steps:
a. Put the TV in standby mode
b. In quick succession, press INFO > MENU > MUTE > POWER
c. Select Options
d. Select Factory Reset
e. The TV will now turn off
f. You must power on the TV yourself
g. The TV will now be reset to its factory settings
3. Now, connect the TV to a different internet connection. To do this, use your mobile phone as a hotspot if possible. (Data charges may apply).
4. Whilst connected to a different internet connection, wait for the ESN to be loaded (may take up to 5 minutes).
5. Now, reconnect to the original internet connection and check if Netflix is operational.
Hope this helps somebody