Exporting Audio

Apologies if this has previously been covered, I did search before posting but didn't find the answer I'm seeking.
Despite having previously exported audio to a WAV file with no problems, I've suddenly started experiencing problems, when I attempt to export all I seem to end up with is a blank file with no audio.
I record mainly in audio and when I export I use;
 
File type - Riff Wave
Preset - What You Hear
Source/Buses Tracks - Saffire (main outputs)
Source category - Entire mix
Channel format - Stereo
Sample rate - 44100
Bit depth - 16
Dithering - triangular
Mix enables - all ticked
 
As I say I've previously exported no problem doing this but now it's not working, which is very frustrating as I'm trying to get an EP project finished.
As with previous problems I've encountered on my Sonar journey, I'm sure this is probably something simple or obvious that I'm not doing, but for the life of me I can't figure what it is??
 
Any advice would be much appreciated.
 
Nige
 

I could be wrong, but I see a possible conflict in your preset/source settings.
 Not everybody does this, but as a hard and fast rule, I always select my Master Bus as the source.
For this to work properly, it is essential that all tracks and/or busses are routed to your master bus before going on to your sound card.
One big benefit of this is the master bus meters give one last look at cumulative levels before export. I also put Voxengo SPAN in the master bus FX bin to check for any stray imbalances in frequencies.
Using this method, your export settings would be:
Preset:None
Source Buses/Tracks: Master Bus
Source Category: Buses
Channel Format: Stereo
Sample Rate:44100
Bit Depth: 16
Dithering:Triangular
Mix Enables: Check all
hth