Bootcamp driver update impossible because Apple Software updater in Win10 gets no connection

Hello!

I tried to update my bootcamp driver (Bootcamp ver.6 installed) to get Retina 5K support under Win10.

When I try to do that with the Apple Software updater in Win10 there coms a Error Message which says: "Can't connect to the Apple Software Update server",

please check Internetconnection...

But Internet is working, Firewall is disabled an iTunes has connection to the store.

Please help!

best regards

Markus