I was wondering if someone could help. I was trying to set up some side chaining last night but unfortunately I could not get it working. I was trying to side chain to the Pro Channel Bus compressor on a vocal track but at first it did not work,(no signal was sent)then Sonar either just crashed or kept getting audio drop outs the second I hit play. I then tried the same with the Sonitus Compressor and also 2 Native Instruments ones as well, but again it either crashed or just froze the audio.
 The signal path was: vocal track> send to new stereo bus> added a delay then Bus Comp. Turned on the sidechain switch
then New send from vocal track to Bus Comp Sidechain. At first nothing happened then it just crashed or just would not play without the audio engine dropping out.
 I also try send other tracks to the the comp but this did work either, and I even tried doing the same with a new track (tried ducking a bass part with the kick drum).
If someone could help with this is would be greatly appreciated as these are things I have managed to do easily in the past and now it seems something is seriously wrong.

It almost sounds like you are trying to duck a vocal track with itself?? Are there two vocal tracks and you want one to "duck" when the other comes in? It would help to know what you want to duck and what you want to trigger the ducking.

I am ducking the vocal with itself so that only the delay comes through on a separate channel. I have done this loads of times before and this is the method that I basically use:
http://blog.cakewalk.com/easy-dynamic-vocal-fx-sonar/
 
I even checked all my settings against this but to no avail (I was using a different delay, but even tried the Blue Tubes was as above just in case it made a difference, which I knew it would not) 

Is the problem only for a particular project, or also if you do it in a fresh project? At least for me, sidechanning is working in Sonar (2017.1) as it should.

i will check over the weekend but I seem to remember having a similar routing issue a few weeks ago in that the sidechain input was not being displayed in the list of sends. I have a feeling I could have a registry problem or something as the other problem was in another project.

I would do a quick test if you can and create a new project with just one ten second vocal track, then try the routing again.
 
For some reason this reminds me of several occasions where deleting the problematic bus and creating a new one seemed to be a fix.
Good Luck!

I might not be understanding your problem correctly but possibly try this:
 
Create 2 busses. Have one bus as the output from your vocal track and the other as a Send.
 
Put the compressor on one bus. Have the output from the original vocal track also sent to the compressor on that bus.
The output from this bus should be sent to the second bus.
 
Use that second bus as a master. You can then duck your vocals with themselves but you've changed the routing so its handled on the way out, and not routed back into itself and should be able to mix as suits. This also allows you to choose where to put in other FX, either on the ducked version of the vocal output or on the master vocal output.
 
I hope that makes sense and helps.

I will try all of these suggestions this evening but to answer Roo, it is not how the routing is being set as I have done this many times before but more that the routing is not working at all. Instead of working it is just crashing Sonar, even when I have tried it on different channels, like I said, I even tried ducking a bassline with a kick drum. As soon as I assigned the send and pressed play the audio engine would just freeze and after a few goes just put Sonar into "Not responding"
 
 

Righty, didn't mean to be teaching to suck eggs or anything, it just wasn't clear to me if it was a routing of the routing issue, or if something was going boom despite being properly set up. Hope you get it solved.

stevesweat
deleting the problematic bus and creating a new one seemed to be a fix.

 
Can't give you a reason, but this has worked for me.