@BES234 A very belated response. I ran into the same problem, after reading at Netflix' forums that Opera is the only Linux browser supporting 1080p, I wanted to use this. Got the same error as you. After checking I had set it up correctly, I vaguely remembered I had to disable Secure Boot to install Linux, with the important reminder I can re-enable it later. So, I went into my computer's BIOS settings and re-enabled Secure Boot, and after that, playback on Netflix through Opera works for me.