Oracle database recovery error alter database open;

knilluz@d6p:~$ sqlplus /nolog

SQL*Plus: Release 10.2.0.1.0 – Production on Wed Jul 14 17:32:08 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.

SQL> conn / as sysdba
Connected.
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup nomount
ORACLE instance started.

Total System Global Area 587202560 bytes
Fixed Size 1260196 bytes
Variable Size 171967836 bytes
Database Buffers 411041792 bytes
Redo Buffers 2932736 bytes
SQL> alter database mount;

Database altered.

SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-01221: data file 1 is not the same file to a background process

SQL>