I had this problem and after countless hours of research and trial and error I finally narrowed the problem down. It worked. It won't be as easy as 1-2-3. I had to keep sanding, and keep trying and finally it worked and stayed working. But this method DOES work.

You'll have to put something on your brake pedal to press it down and then look at the lights yourself to see if they are on. If one of them is flickering a little bit, then you need to keep sanding the metal filaments and try again. The whole process took me about an hour. But there are no more bulb out warnings and all tail lights work and fire up nicely without any flickering or problems.

There's something about driving a BMW and having a tail light out that just doesn't sit well with me. This problem drove me crazy until I finally figured it out...