Both of my tail lights on my 2002 x5 were throwing error codes with good bulbs. Took out tail lamps..easy only three 8mm nuts each. Check metal contact ring (circuit board as they call it) where the bulb socket twists into. The metal ring on mine had small holes melted in it so contact with the bulb socket wasn't good. Also, the plastic welds that hold the metal ring in place were melted so the ring wasn't high enough for good contact either.

What I did that fixed both lamps was to clean the holes to expose metal. Filled the holes with solder, also placed small pieces of heavy duty foil over them. Next I placed a small piece of plastic (from a plastic fork lol) under the metal ring to bring it up to level and melted it in place. Plugged in the bulbs and the connection and it worked for both sides. Finally bolted back on the tail lights.

Took about 15 minutes total to repair both sides. Saved hundreds. This is very easy to fix so try to DIY before going to the shop IMO.