Hi there and thank you for the welcome!
The Server was reinstalled last week.
The Date and Time Settings are correct and the Timezone too.
We are using a internalt NTP Server too, so the Server has exactly the same time as the rest of the System. The NTP Server is our Sophos UTM and it has definitely the right time settings otherwise our whole network would not work correctly.
The BIOS Time is alse correctly set because we enabled the "backwriting" from the OS to BIOS.
We have no network Proxy running, that would block any authentications ...
Any further ideas?
Regards
Christoph