What platform are you running on and what version of SpectraView are you using? If you are running on Windows did you recently update any video drivers, or drivers for the sensor (maybe installed some other application)?
Ok - managed to fix the problem. For some reason it wouldnt work when the existing calibration was turned ON. I turned it off and it worked. I suspect a windows update to the video driver is the cause of the problem.
I really cant wait for my new Power mac desktop to arrive so I can boot Vista and windows out of my life forever.