The preview doesn't work.

You're trying to preview your video but get this message: "Ouch! We encountered an Internal Error. Failed to load preview file." 

You've probably hit a machine which cannot produce the preview at this moment: best is to try a couple times,  close and restart the preview, at some point you will hit another machine that will do the job! Also, when a large amount of videos are being previewed/created by our users this can lead to a shortage of servers' availability.