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Thanks for the Information.
But yesterday in the evening the sites are reachable.
I install and configure the xwiki without a Proxy, and…all okaey.
Now in the Company, behind a Proxy and Firewall i have the Problem as tmortagne detected.
I Need help with the Settings.
Do you know, how can i testing the Proxy Settings?

Hallo Bert,
first try it again, becaus since my last post this morning, the nexus is now reachable.
Is your installation running on windows or linux?
Regards, Ulrich

Are you sure about the upper case letters in the domain name ?

Maybe your proxy requires credentials too ?

right, the Proxy has the same Name. But this is not the ERROR.
Where is the Location for the proxy entrys?
There no credentials for the Proxy.
But we have the Firewall and there is the Port 443 now open.

@Ulrich: Windows2012R2

Thanks for the help,
Bert