Export Audio - puzzle

I have an issue with exporting audio.

I've saved a file - 'Song 1'. This is my pre mixdown file once all song tracks have been recorded.

I go to export audio from this file 'Song 1' and the file is created (exports) without problems.

I begin the mixdown process with Plugins, automation, etc,  save the file as 'Song 1 - Mix1'. I go to export this file to RIFF wave and Sonar shutdowns in less than 2 seconds.

I check the location where I save the file and I see that the file has been saved, however, the file size is only 4kb, instead of the usual 50 - 60 MB. 

I can't figure out why using the same files but saving under a slightly different file name 'Song 1 - Mix 1' after mixing the song, is not allowing me to export 'Song 1 - Mix 1' to .wav file.

Trying to avoid re-mixing 'Song 1'.

Please help.

Maybe a dodgy plugin?

Sonar shutdowns in less than 2 seconds.

What do you mean by "shuts down"? Does the export simply appear to have completed?  Or is Sonar crashing or exiting in some way?

If the first, then try explicitly selecting tracks and time-line in Track Pane before initiating the export, because I think that what is happening is that Sonar is successfully exporting to a wav file, but the wav file is effectively empty, because nothing is selected.  I have never figured out why sometimes you need to make an explicit selection, but when I have made empty wav files in the past, selecting first has always solved it.

If the second, then it does sound like a bad plug, as others are saying.