Replace audio in video file --- help

Ok. When I use the ‘‘replace audio in video file’’ it creates a new video file which I am unable to play (and not load up to Youtube).
This is really annoying. Am I missing something obvious. Anyone know?

Thanks Rob

Yeah. Basic answer is that Cubase is not a video editing/adjusting software. What you can do - with some effort - is to buy QuicktimePro, adjust your video to length there, import this into Cubase and mix your audio. Then, with your audio edited, export the file via the youtube software.

Ha, or you could skip the whole process and edit your clips in Win7 media editor and post to youtube. My point is, Cubase is not for video work.