[DerekM]

And you tried changing the temporary recording location and there's still not any file showing up there?

-What version of OS X are you using?
-What version of OmniOutliner are you using?
-What mic are using for audio recording?
-Try specifying that mic instead of "System Default" in OmniOutliner menu -> Preferences -> Sound Capture -> Input Device
-Do you have a different mic to try if it still doesn't work?
-Does that make a difference?

If not try taking a recording with a different app if you have one. You can use QuickTime if you have 10.6 to do this.