After upgrading to a newer 4D version on a Windows machine, there may be some instances where the 4D server does not show up under the available servers tab or remote clients may run into an error when trying to launch and connect to 4D, despite there being no other structural changes.

Check to make sure that under the structure settings for the server, the server is published on startup and that the correct port number is in use. Afterwards, check to see if the remote user is able to ping the server address from their machine. If all these steps seem correct and there is still trouble connecting to the server, double check the server machine's firewall settings to make sure that there is an instance for the upgraded version of 4D server that gives it permission to be published on the network and discovered by other computers.