$ oerr tns 12203
12203, 00000, "TNS:unable to connect to destination"
// *Cause: Invalid TNS address supplied or destination is not listening.
// This error can also occur because of underlying network transport
// problems.
// *Action: Verify that the service name you entered on the command line
// was correct. Ensure that the listener is running at the remote node and
// that the ADDRESS parameters specified in TNSNAMES.ORA are correct.
// Finally, check that all Interchanges needed to make the connection are
// up and running.

$ oerr tns 12538
12538, 00000, "TNS:no such protocol adapter"
// *Cause: The protocol adapter requested (by way of the "(PROTOCOL=..)"
// keyword-value pair in a TNS address) is unknown. If the supplied address
// is typographically correct then the protocol adaptor is not installed.
// *Action: Install the protocol adapter or correct typographically error,
// as appropriate.  Note: if the supplied address was derived from
// resolving the service name, check the address in the appropriate file
// (TNSNAMES.ORA, LISTENER.ORA or TNSNET.ORA).