Brake warning light flashes
 

I have 2004 X5 with 72K.
my brake warning light flashes on and off, then stays on for some time. I have replaced since rear and front rotors+pads+sensors and add some brake fluid.

I can reset the light (key in position 2 for 30sec) but it comes back after a while, sometimes just blinks (1 min on 5 min off) other times stays on until I do another reset.

What else can cause this light to be on?
Any advice will be greatly appreciated.

Thanks
Jesse