Path Disclosure without ability to read files

What you describe can be called an information disclosure vulnerability. You could use this technique as a method of fingerprinting (looking for specific operating system files, common web framework folders and files, etc.) and could prove useful in identifying a version of something on the system that is susceptible to a separate vulnerability. As you've indicated it's a web server, it could aid in exploring web application vulnerabilities such as arbitrary file upload (if the functionality exists) or otherwise.