There was a small problem with the Grobnik, Croft & Montjuich links due to the move from our old server to the new one a few months back. I've now fixed the series page download links, so please check they now work for you Philipp. They were working if you went directly to our Download section and chose the track from the AC Track lists. The car mod DL link works for me too. Do you still have a problem with that? Do you get any error messages or such like?
I've made a small change so please try again. It was and is working for me both before and after the change . If it still doesn't work can you DL it from this page? https://simracingonline.co.uk/resources/categories/cars.3/