ORA-28546: connection initialization failed, probable Net8 admin error

When using Oracle Heterogeneous Services with Oracle Release 9.2 and up, on Unix (Solaris, HP, AIX, etc.) systems, the tnsnames.ora entry may be incorrectly formatted, resulting in errors like

ERROR at line 1:
  ORA-28546: connection initialization failed, probable Net8 admin error
  ORA-02068: following severe error from HSODBC
  ORA-03113: end-of-file on communication channel

Note the following syntax, differing from that used with Oracle 9.1 and earlier, is required as of Oracle 9.2:

hsodbc =
    (description=
      (address_list =
        (address=(protocol=tcp)(host=hostname)(port=1521))
      )
      (connect_data=
        (SID=hsodbc)
      )
      (HS=)
    )

To resolve the error, edit your $ORACLE_HOME/network/admin/tnsnames.ora file to more closely resemble the above, substituting your actual values for hostname and SID as appropriate.