It is common to browse websites that leak information regarding the technologies they use in various error messages. Attackers can try to willfully raise errors to find those information and have a better understanding of the attack surface.
Practice
Raising error pages and messages can be done manually when browsing the website by doing the following actions
requesting a page that doesn't exist (status code 404)
requesting a page without the proper rights (access control raising status code 403)
supplying garbage (special chars or wrong syntax) in user inputs (parameters, forms, headers) to raise syntax of filter errors.