Replace audio in video file error

  1. I imported mp4 video and audio tracks normally
  2. I mastered the audio track
  3. I exported the audio file
  4. I hit File; Replace Audio in Video File; selected the original mp4 video file; hit open and received this message;

Medium Type not supported or invalid medium

(my signature says Cubase 7 but I am using Cubase 8 now, I’ll change this next)

bumping this hoping someone has a suggestion.