welcome to wiichat, tomc! you'll find it a helpful place.
the most critical and common problem is placement of the sensor bar and setting it's sensistivity, and making sure that NO lights surrounding the sensor bar interferes (you'll see this when you setup the sensor bar's sensitivity)
check out awesome details in your manual, or click below
remember, the sensor bar is just a pair of headlights transmitting to the remote and is only critical in pointing the cursor, not during tennis or bowling play.
the remote senses the bar and transmits wirelessly to the Wii... the bar senses nothing and steadily shines invisible lights for the remote to sense.