when u hit above URL in browser then it prompts for username/password, so that user should have sufficient authz. (user should have SAP_XI_APPL_SERV_USER role).
Secondly, to get detail info abt 500 internal server error check the logs generated at NWA using below path.
Monitoring Internal Server Error 500 Error Responses - Administration - SAP Library
Thanks
Amit Srivastava