That's great you found it, and even better that you reported back what you found. Not everyone does that; it does us no good for the next time when somebody just writes "I solved it.".
Isn't it likely you created the problem the same way you solved it, with a batch command? By the way, the panning would not have mattered if the volume were set to 0.
The way I learned that joke was, there's a dead short between the chair and the keyboard!
One small advantage to version 2011.5 is the better visual feedback on volume and panning you would get from the new mixer, instead of having to hunt for the little numbers. [End of commercial]
CD 2-minute preview. Studio recordings of tracks composed in Band in a Box.