I am not sure how the battery charging controler in the N800 works, but I seem to get the "not charging" message when using an underpowered charger. My guess is that the N800 is demanding more current than the charger can provide.

Initially, I thought my problem was that the Boxwave adapter I was using didn't fit correctly. However, after testing it using different power supplies, I am convinced that the message is do to under powered supplies.

The adapter I use converts USB to the Nokia mini power jack. I always get the message when using my work PC and the Boxwave to charge a less than half capacity N800. If I move to a newer PC in the office the N800 charges without error. Also, I don't seem to get the error when charging the N800 with a near full battery and I never get it with the supplied Nokia charger.