Possible cause: "Gemeinsame Nutzung der Internetverbindung" (Internet Connection Sharing) is enabled on one of your network controllers.
Solution: You must disable internet connection sharing. To do this, proceed as follows:
- Control Panel → Network and Sharing Centre
- For the network adapter LAN connection, open the "Properties" window by right-clicking. Click on the "Sharing" tab and uncheck the box "Allow other users in the network to use this computer connection as an internet connection". Click "OK"
- Repeat point 2 for the wireless network adapter (if available)