Output device setting error

I on a Mac running 10.6.8 on and intel duocore 2 with 4 gigs of ram. I am using Audacity 2.0.3. I got it through a .dmg installer.

I keep getting a prompt “please check output device setting and project sample rate audacity” when I run the sound through my Plantronics usb headset. Works fine coming through the “built in output”.

How can I fix this?

Write down the Audacity project rate bottom left then quit Audacity, leave the headset connected and open /Applications/Utilities/Audio MIDI Setup. Make the headset default input and output, set the sample rate to the same as the project rate you wrote down, and set the channels to 1 ch if it’s a mono headset.