I saw another thread similar to this problem, but not exactly the same. I opened a project from 2 years ago and realized instantly that the whole thing is being summed to mono. I've disabled all plugins, all tracks are stereo, the master output is in stereo, but when I try to pan anything nothing changes, everything is mono, tracks, master, everything.....Any ideas?

Make a copy of this project and delete all plugins in bus or master, one after the other.
There must be an old plugin in a bus or in the master that forces the whole output to be mono.
 

how does it sound if you bypass all effects? (Shortcut is 'e')

Bypassing the effects do not prevent that one plugin forces MONO.
This plugin must be deleted - bypassing or disabling does not help.
I had the same problem.

I'll try that today and see if it works, right now there's no plugins on the master bus, so I can't comprehend how it can be playing back every track in mono.....
 

Probably stating the obvious...
You are aware that panning a stereo track acts just as a balance, aren't you?
The track itself does not move to either side, one side just gets louder/quieter.
To position a track in the stereo field with panning requires a mono track (or
a separate plug-in, as SONAR doesn't have separate pans for left/right channel.
 
But still, the panning should have an effect, of course.

Any stereo track I've ever laid down, behaves just like mono if you pan. In any case, deleting every plug in worked. I really would like to understand how this occurs. The next problem is after I did a Kontakt 5 update a while back it loads in the left channel only.

Did you set the output to all outputs mono? This should be in the setup dialog for that synth. 

Thank you for posting the question, dbm001. This is good to know! I was planning on going back and remixing some old demos (living in the past, I know!) for the fun of it. If the panning did what it did with you, I don't think I would have thought to delete all of the effects. 

Don't forget there is a bunch of panning laws you can set the pan to.