Downloading a file via webclient

While downloading a file via web client -> i am facing an error
Server Error in '/' Application. Access to the path 'C:\Program Files\IIS Express\63076070HSYNCVSDhsync.vsd' is denied. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.  Exception Details: System.UnauthorizedAccessException: Access to the path 'C:\Program Files\IIS Express\63076070HSYNCVSDhsync.vsd' is denied.  ASP.NET is not authorized to access the requested resource. Consider granting access rights to the resource to the ASP.NET request identity. ASP.NET has a base process identity (t ...