TNS-12547: TNS:lost contact

 Hi All,i m stucked with TNS : lost contact error. actutualy i have created a tns service in a 9i (9.2.0.5) database and through this service i m going to connect with an 10g(10.2.0.3) database 

below is my service entry in tnsnames.ora file in 9i database

test = (DESCRIPTION=

                (ADDRESS=(PROTOCOL=tcp)(HOST=xx.xx.xx.xx)(PORT=1521))

                (CONNECT_DATA=(SID=testdb))

            )

but i get 

TNS-12547: TNS:lost contact error when i try tnsping test

one more thing 10g DB Box is behind the firewall. 

please help me out in this regards,

thanks