Connection Xerox 770 – Fiery CWS5 failed, Network settings not visible

Hello!
We’ve got a suddenly appeared connection problem between Xerox 770 Digital Colour Press and Efi Fiery (Command Work Station 5, Windows 7). The CWS is not able to connect to the server probably because of the IP-address. On the other side it’s not possible to change network settings on Xerox 770, because the „Network controller settings“-button in Admin-mode is not visible. Besides the buttons for „Network Scanning“ and „Web Applications“ in Xerox-menu are greyed out. Both machines are connected and sometimes I can ping the IP-address of Xerox 770. Both machines were not connected to the internet, so there were no updates.
Does anybody know this issue? Is it caused by a defect on the Xerox-side or on the Fiery-side?
Thanks a lot for help or ideas!
Julian Mühlbauer