Hi,
I had the following problem in Sonar Platinum (latest available version), so I bit the bullet and installed Cakewalk by Bandlab, which I had been holding off of until now, but the exact same problem remains in CbB.
Every time I initiate Melodyne Region FX on an audio clip, the audio engine switches off, and no amount of clicking or pressing play will switch it back on again. No errors or anything, just a refusal to come back on. Closing the file and re-opening it brings audio back online, and I can then edit in Melodyne without issues. I don't have the problem again until initiating another Melodyne Region FX, which then starts the whole thing again. Anyone else had something like this? Thanks.

What type of audio clip are you applying Melodyne to?

I had that problem. It was a plugin on the track if I recall. In my instance it was REN-EQ
 

Bristol_Jonesey
What type of audio clip are you applying Melodyne to?

Hi, it is a vocal, 24 bit wav file.

bitman
I had that problem. It was a plugin on the track if I recall. In my instance it was REN-EQ
 

Thanks for the pointer, I will check what else is on that track.

Delete all the plugs in that track, see if the problem goes away. Don't save the file or you will loose the plug settings, but at least then you'll know and can trouble shoot further as to which plug it was.
 
I should note that in my instance that plug wasn't a global problem. actually I was surprised as it has been a go to eq for years here.It was just in this file, at this time. CWP files can become "unique" sometimes. If I recall I could re-add that plug and the problem stayed away.

I have experienced that problem transferring MIDI data from EZ Drummer 2 or EZ Keys to the MIDI editor in CbB.  Usually I save the data, exit the project (saving under different project name, just in case) and relaunch.  Usually solves the issue.
 
John B.