Computer Question (Blackburn Neuro)

I've got the Blackburn Neuro 4.0 with wireless cadence, speed and distance, and I'm having troubles with it.  The cadence works fine, but it's the speed and distance that I can't get to register (if you're familiar with this unit, cadence is hooked up to the speed/distance part, which reads the back wheel).  I've tried everything from recalibrating, resetting and reprogramming, changing the battery, etc., and my last thought before sending it back is that maybe it's a magnet issue.  Is it possible to have a dud of a magnet?