I’m having an issue I thought you might be able to help me with….
In audition 3.0
All of a sudden the volume and pan buttons aren’t working. To be clear I can’t get the mouse to make a point in a file where I would drop the volume. It’s weird as it worked before. I can’t even adjust the volume on previous files when it was working….
Is there a setting you know about that prevents this?
One thing to keep in mind is that 3.0 is no longer supported by Adobe, so anything that breaks due to say system differences or being not compatible will simply no longer be fixed 
I know this doesn’t help immediately. I do not know the answer to your question.
As @Izabela mentions Adobe Audition 3.0 is very old and no longer supported. However, something that comes to mind, make sure you’re not working with mono audio files as then you would have no option to pan.