I just went to a project I haven't visited in a couple of weeks. There are several rhythm guitar tracks that are hard panned left and right. They are mono tracks assigned to a stereo bus. They show up as mono wave forms in track view. The pan pot on the stereo bus works fine. The pan pots on the individual mono tracks don't work at all. So if a track is hard panned left, it stays hard panned left regardless of the pan pot position, hard right stays hard right, etc.
 
What would cause this to happen?

My guess is you either set the panning while in Offset mode previously or you set it in Envelope mode, and you're currently in Offset mode (+ symbols on Pan and Volume controls and Offset/Envelope mode button in the Mix module of the Control Bar is lit). Whatever the case, get into Offset mode, center the control, and then go back to Envelope mode and make your adjustment.
 
In earlier versions of SONAR you could inadvertently toggle into Offset mode by hitting "O" on your keyboard. This hotkey was disabled in Platinum, and you have to use the button (looks like an automation envelope) in the Mix module.
 
 

Thanks, Brundlefly. I guess I'm an outlier at this forum for thinking that a virtual console shouldn't be a lot more complex than a real one.

I've experienced this - and Im actually wondering - what the offset mode is used for.  

Raising or lowering the volume of an entire track when automation has already been written and you'd rather not risk attempting to move the entire envelope up/down.

Bristol nailed it - you've added lots of automation to a track's volume widget, but now the entire track's volume needs to be raised or lowered.  You could select all automation nodes and lines (assuming you got them all) and raise or lower them slightly by first increasing the lane or track height for finer control, or... switch to Offset mode and modify the track's fader.    FWIW, there's a "+" displayed next to each applicable widget when Offset mode is enabled.