I can confirm the Logan trailer plays in both Standard View and Theatre View on my Workstation PC (Windows 10 Pro 64bit) with an AMD HD5870 video card (Driver 15.201.1151.1008), running either as a Client of my HTPC, or as a stand alone version of MC. I'm using the Internet Explorer as the Web Browser Engine.
It also plays in both Standard View and Theatre View on my HTPC, which has the specs shown in my signature.
YouTube videos are higher resolution these days, and higher bitrates. Maybe your PC is struggling to cope?
I only get the MC dialogue once in Standard view usually. It plays fine when selecting the "Show the webpage" option, and also plays fine when selecting "Play the file inside the player", although I did get a YouTube error (An error occurred. Please try again later.) show up after playing it inside the player, when MC drops back to the Standard View interface, and YouTube tries to play the next video. But that was YouTube, not MC, or a combination of both. I did see the dialogue pop up twice after receiving the YouTube error, and switching often between the "Show the webpage" and "Play the file inside the player", but the video still worked fine.
Actually, after some more playing, if I play YouTube trailers in Standard View and select the "Show the webpage" option, then let YouTube move on to the next video automatically, the MC dialogue does pop up twice consistently at the beginning of each video. That shouldn't be happening. (I'm using the current Beta version Jim.) Of course if I select the "Keep using this answer" checkbox in the dialogue, it doesn't pop up again at all.
When played in Theatre View there is no YouTube error, and at the end of the trailer MC drops back to the MC view I was in before starting the trailer, which was the YouTube>Search view.
While the above isn't perfect, I think there is something wrong with your setup Audunth. I don't think it is a video driver, since you get the message "File could not be found..." and this issue has persisted through multiple MC versions on your PC.