Why can't I log in to SYSTEM without AS SYSDBA When loging in to sqlplus as SYSTEM, why does the login fail with an invalid username/password error if I do not include "AS SYSDBA"

C:\Windows\System32&gt;sqlplus /nolog

SQL*Plus: Release 11.2.0.1.0 Production on Mon Dec 16 01:00:13 2013

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SQL&gt; conn system/password
ERROR: ORA-01017: invalid username/password; logon denied


SQL&gt; conn system/password as sysdba
Connected.
SQL&gt;


I have a script that I need to run locally.  This script runs fine on other machines, but fails with the error above for me.
Because you are not logged in as the user system. When you execute conn system/password as sysdba, Oracle won't even check the user and password (--> from the local systeem where the db is running on). If you enter the system/password as sysdba and then execute 'show user', you'll notice you are logged in as user 'SYS'. So you are actually entering the wrong password when you execute the conn system/password, Oracle doest not lie.
Check http://docs.oracle.com/cd/B28359_01/server.111/b28310/dba006.htm#ADMIN11046 for more information. Because what I told you is not the whole story.