I sent in a report

Yep, I had this in X2a also. My solution was to save, close project and reopen it. Shutting down sonar completely wasn't necessary for me. Happened in a bus and a track. Report submitted. Everyone should do the same!

"My solution was to save, close project and reopen it"

The same for me.

 
This just happened!
 
(and I'll send in a problem report asap)
 
I just changed the Pro Channel preset on my (soloed) drum bus from "Drums-Warm S-Type" to "Bus Warm Concrete Drums" and I got complete silence.
 
A quick check shows that the Concrete Limiter is registering the Input OK, but there is no output at all, hence the silence:
 

 
 
Trouble is, it's intermittent and not repeatable. I just set up a new bus and inserted the Bus Warm Concrete Drums preset and it's working perfectly.
 
 

 
Arrrrgggggghhhhhhhhhhhhhhhh
 
Actually, ignore that, it's definitely not working perfectly (although I thought so as I was hearing the drums).
 
My new bus is showing this where the Concrete Limiter should be:
 

It was the same for me when i had the problem (input shown in the CL, but no output).

It seems to appear when you use a PC preset including the CL (but not only, maybe)...

 
This is still annoying the hell out of me
 
X2b please

This has been happening all along, and has been discussed many times. The Pro channel has some quirks, but I still love it. Hopefully it will be dealt with in X2b or X3.

 
I submitted a Problem Report but it would seem that I didn't give them enough info, or a recipe to make it happen, so they replied asking for more details (which I've done).
 
Trouble is, it's seemingly completely random.
 
 

This is pretty well documented in both X1 and X2 and a. It occurs mostly when you load a Pro Channel preset into a project that has the limiter ( or the Ca-2a ) inserted in the chain. Restarting Sonar will almost always fix it and 'sometimes' you can re-insert the plug or re-start the audio engine as well. Its surprising that a bug that has been around this long keeps evading the the fix list for each upgrade. I suspect a re-write of the Pro Channel code is not high on the profit margin task list.
 
Its a shame because the Pro Channel effects are really quite good and end up in our productions more and more. The Concrete Limiter and the La-2a emulation are worth the price alone.