Please follow this guide if you're getting errors about your sound device whilst making calls in Skype or Mitel. This is also handy if you only want sound to come out of either your laptop speakers or headset/earpiece.
How to make the sound only come out of your headset or speakers.
Click on the magnifying glass at the bottom left of your screen. Type ‘Control Panel’
Open that up and click on ‘Hardware and sound’
Click on ‘Sound’
Select your headset so that it becomes highlighted, then click “set default”. Click “Ok”.
If you want sound to only come out of your laptop speakers then click on the ‘Realtek® Audio’ options and click ‘Set Default’.