This is an indication that there is something amiss in the lighting department!
It could be something as simple as a blown lamp or somebody could have fitted incorrect wattage lamps. The system is very sensitive so will detect and annuciate as to what a mere mortal may deem to be an insignificant problem.
As advised above a thorough check (best to have an assistant) and hope you find a blown lamp, if not you will need to methodically work around the car examining each lamp for correct wattage.
PS: My most common lamp failures are tail and stops.
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K