From what I've been told by BMW mechanics the tyre (tire) pressure warning system works on a relative rotation system. I.e if over 3 days 3 of your tyres do 3000 rotations and one does 3200 rotations then it senses that that tyre's pressure is lower (I don't know what the threshold is). If you do a lot of low speed turning in one direction I.e driving around and around a parking lot then from what I can gather that could cause a false error. If you do that then unfortunately there is no "cure" other than disabling the system (which I don't know how to do).

Not much help I know but I thought that by putting in my 10 cents on how the system works it may help you with diagnoses.

Good Luck

Andrew