When i try to start BOINC, the manager asks me to attach to a project and asks for a url. When i give the "https://boinc.bakerlab.org/rosetta" url, the
manager tells me, that "The url you supplied is not that of a BOINC-based project. Please check the url and try again."
I have checked and i have tried.
What is the right url?
(The "https://boinc.bakerlab.org/rosetta" is the one i received with the account key.)

OK. It was a setting in my firewall, that blocked the traffic. So, the problem is solved!