2001 X5, Bottom rear tail light replacement

[ike301]

So I tried replacing the bulb, and actually the original bulb in there, the filament was not even broken.

but the light doesnt work. i put in a new bulb (sylvania 7506(p21w) BP) and it still comes up 'rear light' error on the dash.

any ideas? i tried cleaning the metal parts (just brushing it with some saliva on my finger).

the original bulb has only one filament, not two like the higher brake light.