Wow this tip with a wrong typo or unsupported letter or sign in one of the folder names inside the Community folder actually worked!
I put the contend of the Community folder in my Flight Sim Add-on Backup folder - and suddenly the marketplace is fully functional again 
Finally I can download this England update!
Perfect. Thanks for this tip.
But one question remains… with hundreds of folders in the Community Folder only having englisch letters (so no Ö or Ä or Ø and because it is impossible to put a " or ° or ` or whatever special sign in a folder name, none of these signs appear)… which one of my mod folders is the culprit preventing the marketplace from loading?
I guess no one will ever know 
:
Well finally I can buy a Carenado planes and download the UK update.
