A file has been uploaded to a website's document root directory (or one of its subdirectories), but an attempt to access it produces the "404 Not Found" error. Other files in the same directory can be accessed without problems.
The file has an extension for which the MIME type is not configured in IIS by default. Such a problem may affect JSON data files (extension .json) or MPEG-4 video files (extension .mp4). Other file types may be affected as well.
Configure the appropriate MIME type for the file's extension on a server level through IIS Management Console. Refer to the following links to get detailed instructions: