Hmm, are you trying to add just audio? You'll need to use software to merge your audio track with your video to create an mp4 file. If it's not just audio, let us know. We'd like to look into it further.
Appreciate the follow up, the best next step for these types of issues is to reach out to the Creator Support team. Here's how you can get in touch with them: http://yt.be/help/partners . Hope this gets resolved.