A connection to the web server could not be established

If a workbook cannot connect to the server, you are limited to working offline.

One reason why users may be unable to connect to the server is the Decision service URL in User Preferences is invalid. See also "Repeated Prompts to Sign In or 'Connection…Could Not Be Established' Error".

Another reason is that the Decision service is not running. If the Decision service is not running, you must manually start the service.