Server Version#: 1.20.1.3252
Player Version#: 7.7(21764)
I am unable to play lots of movies in Plex. All in MKV container. I do not believe it to be a server error. I can use Infuse 6 client to play the files in question.
The error is the transcoder exiting due to an error. I have confirmed both the new and old player.
Anyways, I decided to move my temp transcoding directory to an SSD. Inadvertently that seems to have solved my problem. I can only suspect that if you are having similar problems, there may be a permissions error with your temporary transcoding directory.