Well, I searched the boards over at ShinyWhiteBox.com for the error I was getting and I found a number of folks bringing this issue up. Neil, the admin over there, responded to the threads and never really offered a solution.
So I e-mailed Neil about the issue. He said he had never heard of it. He suggested that I purchase and use their Stomp audio application to seperate out the system audio from the MOV file.
I responded that I did not want to add additional steps to my process and that I felt that purchasing another application from them was not a reasonable solution. I also pointed out the numerous threads on his website that he has responded to that detail this issue.
That was a couple of days ago and I have not heard a word back. So, it's on to SnapZ Pro I go. At this point, I have to say that if you have a need to record your session on the Mac and you want to be able to capture not just the video and your narration, but the system audio as well, do NOT buy iShowU.
I did a concept test of the Zombie Debt commercial to show to the client. I was on the phone with them when they played it last night and I could hear them laughing like crazy. They love it and we are moving forward with this concept.
This weekend I will record and post the Soundtrack Pro audio cleanup tutorial and get it posted up here.
Stay tuned :)