Error

From: rucha <rucha.shrivastava_at_gmail.com>
Date: Tue, 22 Dec 2009 07:06:04 -0800 (PST)
Message-ID: <cb198901-7148-4988-95b7-35bbded16f2a_at_r24g2000prf.googlegroups.com>

how to overcome with this error???

SQL*Plus: Release 8.0.3.0.0 - Production on Tue Dec 22 20:26:57 2009

(c) Copyright 1997 Oracle Corporation. All rights reserved.

ERROR:
ORA-12203: TNS:unable to connect to destination

Whenever i write username:scott

and                    password: tiger

then this error occurs.
Please help me out!!! Received on Tue Dec 22 2009 - 09:06:04 CST