Cause: The protocol specified for an externally-identified outbound connection from a shared server (database link) was not the same as as that used for the inbound connection. It is not possible for Oracle Net to authenticate a proxy connection that uses a protocol that is different from that which was used for the connection to the shared server. See the solution below.

Error solution: Specify the same protocol in the Oracle Net connect descriptor for the outbound connection as that used for the inbound connection