The SampleCell Editor uses the computer's sound capabilities to do previews. Consequently, there must be a valid sound card available for sound previews. If the computer's only sound card is a Digidesign card that is in use by an audio application such as Pro Tools, then there will be no sound card available to SampleCell for previews. One way to avoid this is to go to Pro Tools' Operations Menu, and UN-check Active in Background (this will free up the hardware once any other application is made active).