"/ as sysdba" Failes But "sys/password@service_name" Works ???

I'm trying to connect to a remote Oracle database from a Unix box.

Unix : AIX 4.3.3.
Oracle: 8.1.7

$> sqlplus sys/syspassword_at_my_db_name

Connected.

perfectly works

but, the following commands generate ORA-12545: error, any idea why ? :

$> export ORACLE_SID=my_db_name
$> sqlplus "/ as sysdba"

ERROR:
ORA-12545: Connect failed because target host or object does not exist

i.d. Received on Wed Feb 25 2004 - 13:54:27 CST