There are a number of reasons why this may be happening. The IP address must be unique to that instrument, but at the same time the PC through which you are trying to communicate must be on the same network. In the case of the Screenmaster paperless recorders the unit must be power cycled after a change to the IP address otherwise it won't recognise it. Always make sure that you Ping the unit before attempting to access the webserver or FTP server of a unit. This ensures connection is good and tells you if the other features cannot be accessed that it is a windows setting rather than a fault with the unit. If you are unable to isolate the cause please contact your local ABB representative.