In the context of web development, what does the error message "Access to XMLHttpRequest at from origin has been blocked by CORS: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource" indicate?
A) The web server has encountered a timeout issue during the request.
B) The client-side script has encountered a syntax error in the code.
C) The server is not configured to allow requests from the origin of the requesting client due to Cross-Origin Resource Sharing (CORS) policy restrictions.
D) The requested resource is not available on the server.