There can be a problem with moist in the lock sensor on the boot.
Like you would close the door and the locks would close but open
again after a few seconds. This mostly happens in rainy weather.
You will also see that when this light is burning you cannot operate the
central locking system, not even with the key!
It's usually caused by moist thay runs into the part of the lock that is
in the trunk lid. Quite normal at wintertime.
You can solve it by carefully putting a screwdriver between the 2 plastic
halves of the lock cover and blowing hot ait in the lock with a hair blower
and dry it out.
You can also solve or even prevent this by using a CRC 5-56 (or WD40)
spray on the sensor.
Thanks to Gert-Jan for this info.
Thanks to Stein Erik Hanssen for the tip about the CRC 5-56 spray