Message Oracle ORA-28544 - connect to agent failed, probable Net8 administration error

ERRORconnect to agent failed, probable Net8 administration error
CAUSENet8 reported a failure to make a RSLV connection or a protocol mode error when the Oracle server attempted to establish communication with a Heterogeneous Services agent or an external procedure agent. This usually is due to an administration error in setting up Net8 service definitions in TNSNAMES.ORA or LISTENER.ORA: A basic network connection is opened, but it connects to a program which does not use the appropriate protocol. This often is a sign that the connection goes to the wrong program.
ACTIONCheck Net8 administration in the following ways: -- When using TNSNAMES.ORA or an Oracle Names server, make sure that the connection from the ORACLE server uses the correct service name or SID. -- Check LISTENER.ORA on the agents host machine to assure that the service name or SID refers to the correct agent executable in its (PROGRAM=...) clause. -- Confirm in TNSNAMES.ORA or the equivalent service definition that sevice extproc_connection_data does NOT contain (HS=), or that the service definition used by a Heterogeneous Services database link DOES contain (HS=).