SAP RFC Destination type G error

Hi,

SAP PI dual stack 7.31 testing a RFC Destination of Type G (Exernal http server) getting NIECONN_REFUSED. Extenal http server requires username and passowrd in header field "Authorizaiton = Basic "username:password" in base64 encoded. In RFC Destination I am using basic authorization option where I input username and password but it giving NIECONN_REFUSED. Can you help me on how can I achieve this.

Thank you,

Mallik