can't connect locally through Net8

I can connect remotely from other tools (Toad, Oracle for NT), and I can connect by just typing:

connect system/manager ...

but if I try to connect through:

connect system_at_lat

I lose - and it fails.

My SID is lat, and i defined my tnsnames.ora as:

AT.CONCRETEMEDIA.COM =
  (DESCRIPTION =
    (ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    )
    (CONNECT_DATA =
(SID = lat)

    )
  )

and my listener.ora is:
LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = latdev1.concretemedia.com)(PORT =
1521)
)

    )
    (DESCRIPTION =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))
    )
  )

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
(GLOBAL_DBNAME = lat.concretemedia.com)
(ORACLE_HOME = /u01/app/oracle/product/8.1.6)
(SID_NAME = lat)

    )
    (SID_DESC =
(PROGRAM = extproc)
(SID_NAME = PLSExtProc)
(ORACLE_HOME = /u01/app/oracle/product/8.1.6)
    )
  )

But alas - I cannot get there from the local machine. It is 8.1.6 on redhat Received on Fri Jul 07 2000 - 16:24:11 CDT