When saving a tiddler in TiddlyWiki to a TiddlyWeb server if you see the message: "Error saving
title: connection could not be established" it means that the TiddlyWiki is unable to reach the TiddlyWeb server.
The most likely cause for this is that server_host has not been configured in tiddlywebconfig.py. In order for the tiddler to be able to saved back to the server, the TiddlyWiki must have been told, when generated, the server to which things should be save.
Without additional configuration, the default server host is
http://0.0.0.0:8080/ which is only reachable from a browser running on the same machine as the server. For anything other than testing or personal use, this is unlikely.
See server_host to determine how to make changes.