On my 2008 vw rabbit the brake light goes on and it says rear right and left brake light out but when I brake the brake lights work. Why does it show that its not working when it works?

do all functions of that lamp perform as they should? A lot of lights have two filaments that act as two different functions that run from the same indicator (parking lamps will usually use the dimmer filament and the brake/turn signal will use BOTH filaments) .

dave expalins this well and he is correct it is probly a broken filiment in your light check all your light settings and you should find that light thats out.

Thanks guys but all the lights work good.

did you physicly remove the bulbs and check every single one ? if not do so. Also check your rear light panels (the board the lights come out on) for signs of rust and corrosion. if this is not hte case start tracing wires and check your fuses and relays.