Hi Jaap,
the problem is that the frequency was changed a few yers ago. There is an updated bgl-file on Vatsim:
http://nav.vatsim-germany.org/files/edgg/charts/edll/public/EDDK_ILS32R_AIRAC1311.zip
This fixed the problem for me. I use Aerosoft's German Airports 2 but in the readme.txt it says that the update will also work with the FSX stock scenery.
Peter