If you believe you have the correct FQDN or hostname of the Web Client system, then check the following:
1. Ping the hostname (it may not always work)
2. Perform an nslookup from command prompt. E.g. nslookup <name of server / FQDN>
3. Login to the Web Client system and check the hostname. Also ensure that the service is running on correct port
4. On the Web Client system, navigate to <client_install_directory>/apache-tomcat/webapps/deui/common/scripts and open the 'config.js' file. The file will have the entry of the Client server name (highlighted in red below). It must match the FQDN that is being used by users on the browser. E.g.
If you are going to use the FQDN, then make sure the above line has full address after integSrv.
Note: Backup the files before making any changes. Do not add or change the lines when adding or changing the hostname. Do not remove or change /de after the address and port of the Client server.