I recently received the dash message about the brake light bulb error. After trawling forums, and reading the scare stories of wiring looms or ballast resistors, thought I'd check the bulb. I managed to release the rear brake light easily by: removing the trim from the inside opposite the brake light (just pulls off), then using a torch looking into the holes, pressed the metal clips with my fingers and the light unit simply pushed out. (Don't bother removing the bulb housing from the light unit while it is fitted to the car, as you won't get it back in without removing the light unit anyway). When I discovered the bulb blown (12V 16W wedge type), I replaced it with a 5W version as I thought it might be a temporary fix to eliminate the error. The light came on, flickered a bit, then went off and the dash message re-appeared. I then learned the computer checks the current drawn and the 5W bulb is not drawing enough current, so the computer sees an error. I purchased a 16W bulb from eBay for a few pence and now fitted, the error has gone and the high level brake light is back. Long story short, although the capless fittings are the same, use a 16W bulb, not a 5W (common) bulb.