YouTube Premiere not working?

My UHD mp4 video's won't play when I schedule them for YouTube premiere release. I get a message saying the video type is not supported by my browser (IE), but when I take the premiere option off the video plays absolutely fine however it's listed.

Now using a different browser is not an option as this is the browser my work uses across the board and the video is for work colleagues. I'm just a bit stumped as to what enabling the premiere feature could possibly be having on the video!