oracle 9i problems.. renaming datafiles

Hi

I am trying to rename a datafile in oracle 9 release 1. I perform the following steps but somehow it fails and i have to perform media recovery . when I try and rename the datafile its say that some process is using in , so when i try and bring it online it says it needs media recovery

 any help would be appreciated
Mike

SYS_at_PRACTICE> alter database datafile 4 offline;

Database altered.

SYS_at_PRACTICE> alter database datafile 4 online; alter database datafile 4 online
*
ERROR at line 1:
ORA-01113: file 4 needs media recovery
ORA-01110: data file 4: 'C:\ORACLE\ORADATA\PRACTICE\INDX01.DBF'

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Mike Desouza
Archoak Consulting Limited