Hi Ulrich,
Earlier this summer (mid July) I had a similar problem in interacting with Wolfram Demonstrations. Windows 8.1. After installing Mathematica 10.2.
It was solved by waiting a couple of weeks, until a new installer had come out. Then reinstalling Mathematica 10.2.
Details of the problematic version: 10.2.0 5353456
My current, working, version:
I have since then upgraded the PC to Windows 10. No problems.
