Not able to connect Oracle database, When issue command — > sqlplus “/ as sysdba”

[oraprod@oracle-dba ~]$ sqlplus “/ as sysdba”
SQL*Plus: Release 10.2.0.1.0 Production on Wed Jan 22 02:09:17 2014
Copyright (c) 1982, 2010, Oracle.  All rights reserved.
ERROR:
ORA-01031: insufficient privileges

SOLUTION:

SET CORRECT ORACLE SID
———————-
export ORACLE_SID=PROD         — LINUX
D:\oracle>set ORACLE_SID=PROD  — WINDOWS

SET ORACLE_HOME
—————
export ORACLE_HOME=/u01/oracle/product/10.2.0   — LINUX
set ORACLE_HOME=D:\oracle                                           — WINDOWS

SET SQLNET.ORA FILE
——————-
Check sqlnet.ora file for SQLNET.AUTHENTICATION_SERVICES parameter. It should be set to NTS for windows and for linux set it to ALL.

SQLNET.AUTHENTICATION_SERVICES=NTS  —WINDOWS
SQLNET.AUTHENTICATION_SERVICES=ALL  —LINUX

Please reproduce the issue and see if it resolves !!