Can anyone advise? Whenever I complete a multi-track project, I like to do one of two things: either export the entire mix as one WAV file, or bounce the mix down to an empty track. But today neither of these will work. No matter what I do or try, X1 insists upon exporting or bouncing each track individually... one after another after another. This has never happened before - I have always finished with one track. 
I have selected "Entire Mix" in the dialogue boxes... so what is going wrong? 

have you applied the X1 Updates ?
I believe there is 4 of them which I also believe are cumulative (Updates X1A Thru X1D)
Also check your Bounce/Export settings.
 
JMO, But I have found typically export and bounce abnormalities can sometimes be traced back to soundcards.
What are you using for a soundcard and what version of windows ?
 

Hello Chuck
I am re-installing the updates right now, just in case. I use an Edirol UA-4FX external soundcard. It has always coped before. Baffling.
Thanks Chuck.

Unfortunately, re-installing the updates has made no difference.
Mark

which version of windows are you running ?

Windows 10

That might the problem, or possibly and update messed something up.
Sonar X1 was designed to run on Windows XP and windows 7. It will have worked on Windows 8 im guessing as well but windows 10 is a different animal all together.
In other words, its not supported. When did the problems start ? I would check windows update for recent installed updates as well as look for/ or reinstall the soundcard driver.
 
To rule out your soundcard all together, just unplug it and try to bounce using MME for the moment just as a test.
If all goes well you know its SC related.

Thank you so much, Chuck. I will do exactly what you suggest.
Cheers
Mark

What is your Source? If the source of the export/bounce is Tracks, it will export or bounce each track instead of the single mixdown you want.