stac

sharke
All you have to do, if I'm not mistaken, is select ONE of the tracks which has a send to that bus, then do the export. When you select "buses" from the source category, it will list only the buses that the selected track has active sends to. Usually I'll only have a maximum of 3 or 4 active sends on a track so it's really no trouble at all to just deselect all but the one I wish to export. Although I agree that none of them should be selected by default.  

That's the exact scenario. It does NOT work - that's why I'm posting here.

See the edit in my post above, I was mistaken and if you want to export the whole output of the bus in your mix then you have to select ALL of the tracks which have sends or outputs to that bus. This makes sense because you might not wish to print all of the tracks which go through that bus. 
 
You cannot just select a bus and do an export. You have to tell Sonar which tracks you want to feed through the bus to make the export. I guess it would be nice if exporting the selected bus would by default export the bus output of all tracks which go through that bus, but that's not the case. As far as I know you have never been able to export a bus without selecting the tracks you wish to play through it. 

Selecting in the timeline will select whatever track/bus has focus, and if it's a bus, you'll get the "selection" contains no audio" error. You need to select nothing, and, as Steve said, SONAR will automatically export through the length of the project. If you want more or less than that, you'll have to break down and select the tracks that feed the bus, or as I said, solo the bus without selecting it, and export Main Outs. If there are FX on the Master bus that you don't want, you'll need to go back to exporting with Source = Buses, and deselecting the ones you don't want. I usually take the time to do it this way.
 
This can all be a little unintuitive, but I'm pretty sure it's all working the same in Platinum as in X3

brundlefly
Selecting in the timeline will select whatever track/bus has focus, and if it's a bus, you'll get the "selection" contains no audio" error. You need to select nothing, and, as Steve said, SONAR will automatically export through the length of the project. If you want more or less than that, you'll have to break down and select the tracks that feed the bus, or as I said, solo the bus without selecting it, and export Main Outs. If there are FX on the Master bus that you don't want, you'll need to go back to exporting with Source = Buses, and deselecting the ones you don't want. I usually take the time to do it this way.

 
Thanks for that explanation. It's good to know that Sonar will export the whole project by default - however, I do want it to always export the time selection because it has to be bar-aligned for further processing in another DAW (and sending it off to colaborators).
 

This can all be a little unintuitive, but I'm pretty sure it's all working the same in Platinum as in X3

Hmm, all I know is that I was able to export the whole mix that way (i.e. from a single bus) before (in Platinum), I'm just not sure which combination of selecting/not selecting tracks in the arrangement view did the trick.
 
It would be nice if I had to do nothing at all in the arrangement view but be given all necessary options in the export dialog. That's how many other DAWs do it, and I think that's the most comfortable way. Maybe something worth thinking about for a future Sonar update.

I'm in a different project now, and exporting works, when I select nothing, like sharkey and brundlefly stated (however, with the unfortunate pre-selection of ALL tracks and busses in the export dialog that always need to be deselected manually and one at a time).
 
I have yet to try it in the original project that I had the problem with, but I assume that either I did something wrong, or some strange hickup happened in that project.