This error occurs when the client requests a file with a certain file extension and then specifies the Accept header with ...

This error occurs when the client requests a file with a certain file extension and then specifies the Accept header with a MIME type that is different from the configuration of this file extension on the server. An example is requesting a file with the .doc extension and specifying an Accept header with text/xml instead of application/msword. Usually the client specifies */* for the Accept header, which allows the request to serve any MIME type.