ORA-20000

Use the following:

SQL> connect / as sysdba
SQL> alter user  identified by ;

Action:

C:\>sqlplus /nolog

SQL*Plus: Release 11.2.0.3.0 Production on Tue Oct 29 15:08:10 2013

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

SQL> conn / as sysdba
Connected.
SQL> alter user sys identified by oracle;

User altered.

SQL> exit

SQL> conn sys/oracle@sieb361 as sysdba
Connected.
SQL> exit;