BMW Repair: E39 97 523i Faulty Bulb warning light on dash, trailer lights, warning systems

Question
Hi, prompted by the dash I have replaced bulbs not working and checked all others but I still have both rear lights warning on the dash - Is there any easy fix for this?

Answer
These bulb warning systems are sensitive to the current flowing.  Have you hooked any accessories up, especially trailer lights, or something?  The second pass is to use bulbs from BMW if you haven't...small changes can affect these warning systems greatly.