The SendError method sends a response to the 
          client indicating that an error has occurred, providing a numeric 
          error code and HTML formatted text which may be displayed to the user. 
          The Message parameter should provide a brief description of 
          the error that will be included in the output sent to the client. Note 
          that the message should not contain any special formatting control 
          characters or HTML markup.
          This method provides a simplified interface for sending an error 
          response to the client. In some cases, a browser may choose to display 
          its own error message to the user in place of the generic HTML 
          document generated by this method. If you want your application to 
          send a customized HTML document for a specific type of error, you 
          should use the SendResponse method.
          If you wish to redirect the client to use an alternate URL to 
          access the requested resource, it is recommended that you use the
          RedirectRequest method rather than sending an error response.