Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your node was about to start serving, but it could not get its project ready, so it never opened the port. Let's see what it does first. When you run rush node serve with a project script, the engine finds the manifest, and parses the script. That is how the beings in your project are born, each with its permission and protection settings already in place. This must happen before any remote node can ask for anything, because a remote read has to be judged against those settings. If the script fails to parse, the node cannot serve it. Likewise, if you use publish to share a payload, but this thread owns no being with that payload, there is nothing it is allowed to publish. In both cases, rush refuses before the port is opened, so no one ever connects to a half-ready node. The message shows the reason in the second slot. Fix the script's parse error, or publish a payload you really own, and start serving again.
Text from the Rush engine's error catalogue.