After creating a new XPage in a local database I want to preview it in a web browser but get an error 404 in the browser (File Not Found)
The problem was caused because I have another piece of software on my system that uses the default HTTP port (80).
To fix the problem, change the port used for the web preview in Domino Designer preferences:
From Domino Designer go to File -> Preferences -> Domino Designer and then in general section change the web preview port to something that is not currently used like 8080.
Then preview the page again and the problem was resolved.