We struck an interesting issue this week. One of the schools that have sourced equipment through 3Pi reported that they couldn't get the system to work in one of their classrooms.
The classroom setup was unusal in that the projected image was quite high (above the floor).
They had been trying to calibrate from desk height aiming the wiimote up, but it just wouldn't calibrate.
When we looked upwards along the top of the wiimote, to the middle of the screen, there was an incredibly bright reflection. It seems that the combination of a steeper than usual upwards angle and a very reflective screen were confusing the wiimotes camera. When we tried the wiimote positioned at double the height, it calibrated perfectly, as it also did when we positioned it up by the projector looking down. (Another issue for such a high setup is that only very tall people could interact with the image anyway - not good for young students!)
If you have this problem, or during calibration the four calibration marks seem to click themselves, it highly likely that there is too much infrared light in the room. When using SmoothBoard, you can easily check this with their calibration assistant. At the bottom of the image to the left, it says, "IR dots". There should not be any number by this until you use your pen. Try clicking on your projected image (with the software running), and look at the "IR dot" count. It should show "1" when you click and nothing when the pen is off. You will also see a little dot on the white tracked area. This dot matches where your pen is clicking on the screen - very handy thanks Boon Jin and SmoothBoard! If there are dots floating about when you haven't clicked, you either need to lower/remove the source of the stray IR light or use the software control panel
to turn down the sensitivity of the wiimote's camera. To do this you click on "Show settings", then "Wiimote" after which you can experiment with levels. Earlier posts that we have made on 
this subject are - Fluorescent lights, Crazy mouse.
