Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your manifest says where the program starts, and the engine looked, and it is not there. A manifest can name its entry with the entry setting, when the entry is not called main. If the setting is absent, the default name is main. When the setting is present, rush looks under src for that name, with or without an extension. So what happens if the name you wrote does not match any file? The engine could fall back to main, or to the three dots file, and run something. But that would run a program nobody named. You said one thing, and the engine would do another. That is a bad kind of help. So it refuses, by name, and the message shows the setting and the directory it searched. The fix is simple. Either correct the entry name in the manifest, so it matches a real file, or rename the file under src so that it matches the manifest. Say it once, say it right, and the project starts exactly where you pointed.
Text from the Rush engine's error catalogue.