.mkv video causes :(

Many .mkv videos work fine: first time I have seen this problem: screen displays a sad face.

Questions:

  1. Has anyone experienced this problem? Lessons learned?
  2. How to determine if this is a codec problem?

To get a better understanding of the problem you are experiencing we need more information from you. Please see http://osmc.tv/wiki/general/how-to-submit-a-useful-support-request/ for advice on how to help us.

Can you play the .mkv on a different device?

What does ‘ffmpeg - i .mkv’ report?

That normally indicates a more serious issue (e.g. Lack of power supply or Filesystem issues)
As people said before provide debug logs and also as mkv is only a container format provide MediaInfo for the problematic file.

Please see the mediainfo section in How to submit a useful support request - General - OSMC