Video Wont Play in video editor after replacing audio

I have a video clip for which I recorded the audio into cubase. After syncing in cubase and then successfully replacing the audio in the video I have run into a problem. I am on a Windows machine. I have installed quick time (which I am p***ed about having to do since it is a bunch of bloatware crap and forcing me to use it makes me want to ditch cubase when it comes time for me to upgrade… but I digress). So once I have replaced the audio, I can play the clip fine in media player classic and windows media player. But when I try to edit it in Corel Video Studio, it doesn’t accept the file. It says it does not recognize the format. It is AVI. However if I try to add the unchanged clip (i.e. one that hasn’t had the audio replaced by cubase) to video studio, it accepts it fine. Both AVI files. Same video. But one has the audio replaced by cubase and now it isn’t recognized. Windows media player opens it too. Any ideas?