"Replace Audio in Video" renders video unplayable.

When I use the Replace Audio in Video command, selecting an .avi file I was able to view in Cubase and any other player, and replacing the audio with a new voiceover, a .wav file I exported from Cubase, the result is that the video becomes unplayable. In Windows Media Player, I hear the new voiceover, but can’t see the video. My video editor, Camtasia, says the new file I’ve created is now unsupported. Can you let me know if there is something I’m doing wrong, if this is just a bug, or if there is a fix for this problem etc? Thanks - Rosanna

I don’t do video myself, but from what I’ve been reading here this is expected behaviour. People seem to just edit/ compose/ record the audio to the video in Cubase and then reassemble in a real video editor.