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Thank you Nabruk, your solution worked. I bought the ATV 4 two months ago and downloaded Netflix app and since then I kept getting the same error 11800 when I tried to play any content. I tried each and every trouble shooting steps that Netflix, Apple, my ISP & other forums recommended and none fixed the problem. Until I came across this forum while searching for answers and tried your solution. Changing the DNA manually to a similar DNS setting of other device I had connected to my WiFi network worked just fine.

Great to hear, thank you for the feedback!
 
After trying all solutions I could find on the forums with no result, I've solved the problem with my ATV by manually entering the DNS settings to it similar to DNS settings of other device i had connected to my WiFi network. For some reason the automatic DNS settings of ATV were the cause of the problem 11800 with Netflix.

Thank-You! This also worked for me.
 
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