I have the same exact problem. I also have the same television (Samsung KS800) and Roku ultra. As you might have already searched, most of the solution pertaining to this problem recommend that you restart the roku or/and unplug and replug the hdmi cable. This does help for a while but then the hdcp error comes up again and again, and it's a pain to have to restart the roku each time this happens. What seemed to help me so far was switching to a different hdmi cable - I had an old one on hand which I bought a long time ago; there is no name on it, but it worked better. In the beginning, I did not want to use my old hdmi cable because I thought it might not be 4K compatible. I bought a new hdmi cable that says "4k Capable and High speed - Ethernet" when I bought my Roku, thinking that it would be better. I always thought that all hdmi cables were the same since most reviewers on the web says that it is all 1's and 0's so the cable does not matter so I bought a cheap Vizeo cable at Walmart. However, when I switched to my old hdmi cable the hdcp error decreased. It did not go away, but I only occurred very rarely ( 2 days have gone by without an error) whereas the Vizeo cable caused the hdcp error to occur every few hours. With my old cable (which has much better construction than the Vizeo), there are a few instances where the screens blacks out for 1/2 second and I think I am going to see the purple hdcp error but it goes back to normal and there is no error. So what I think might be happening is that the new 4K information is much more difficult to transmit through the hdmi cable and there are instances where if the cable is poorly constructed it my cause a loss or error of information being sent, causing the hdcp error to occur. I might try some new cables next time with better construction and probably switch to a shorter length ( I am using a 6' right now) to see if this reduces the black screen glitches and hdcp error occurance. I hope this information helps. I am in the same boat and it is frustrating, but please let me know if anyone have any other suggestions or know of a good hdmi cable that has worked for them.