Project won't play

Had a new problem yesterday. A project I've been working on for a long time stopped responding to Play. No response to the space bar, no response to clicking the Play button.
 
I had only opened the project to listen to it, i.e. I hadn't made any changes at all.
 
Tried arming a track and pressing Record; still no transport. Toggling the Pause button did nothing.
 
I loaded several other projects and they all played normally. I copied and pasted everything from the problem project into a new file, and it played normally. Of course, I lost all my routing, effects and soft synths.
 
Has anybody seen this problem?

Thanks scook, I'll give that a try.
 
It seems like a long shot since the file played fine the day before and nothing was changed, but it's worth a shot.

OK, the problem came back. And I found a sort of solution.
 
I opened the project to work on it and transport didn't work.
 
My default audio settings are 48kHz / 32 bit. This particular project was created by a collaborator who always uses 96/32. 
 
I closed the project changed my default to 96/32 and re-opened the project, and it worked fine.
 
Not really satisfied with this, because I don't understand it.

I'm using an RME UFX, as indicated in my signature. Of course, it does AD/DA at 24 bits, but the file bit depth in Settings is at 32 bits.

Make sure the timing masters are set correctly in Preferences > Audio > Driver Settings
 

vanceen
Thanks kev999. The problem isn't no sound, it's not transport. Play (neither the space bar nor the button) doesn't do anything...

 
Having no playback doesn't necessarily rule out my suggestion about the "None" bus output. The audio engine won't start if there is nothing routed to the audio interface.
 
By the way, you haven't mentioned whether the audio engine is engaged or not. I presume that it's not.

vanceen
...There was no indication that the audio engine was not engaged, i.e. no pop-up message.

 
I believe that the popup message you are thinking of is the one that appears when the audio engine suddenly cuts out. If it's not engaged in the first place then you won't see any message.
 
Look at the Transport module of the Control Bar. The symbol in the lower left corner is the audio engine indicator. Is it on or off?

kev999,
 
After switching back to my standard 48/36 setup, I had the transport failure again with the same project.
 
You are correct, the Audio Engine is off. Clicking on it does nothing. I didn't find any solution apart from changing my default settings in Preferences back to 96/32, closing SONAR and restarting.
 
The RME UFX is a great piece of equipment but it doesn't seem to like sampling frequency changes. The Fireface 800 I had previously was similar. I guess that's at the heart of it, but I still don't know why the transport / audio engine off problem started happening with this project, as I've been working on it for more than a year.