Hi
There have been some posts relating to this problem. It also seems in some cases to be associated with previewing the work from the start of the timeline after using the I< button followed by Play. where there is repeated judder of the red cursor line with no sound in preview until Play is pressed again.(Does this happen with yours?)
In these cases the export has no sound. It seems to be connected with Audio tracks and Video clip tracks starting together.
Tests on some downloaded faulty projects have shown something wrong and NCH are currently looking at this problem.
Check out this thread...
http://nch.invisionzone.com/topic/25912-no-audio-when-exported/
You will see that I have suggested the following temporary solution, and it may work with your project.
My suggestion until the developers can find what this problem is, is to split off 1 frame from the start of the timeline.....
Zoom close into the start of the timeline.
Set the red cursor line to the start using the I< button
Step along 1 frame using the I> button
Click the red cursor line again to get the scissor pop up with the brackets
Click the Red bracket to remove 1 frame from the start of the timeline and automatically close the gap.
The single frame deletion won't be noticed and the sound will now export.
It would be interesting to know if that works for you.
Nat