Datafile of tablespace with rollback segment lost!

Hi all,

 I have accidentally deleted a datafile of a tablespace wish contains only
one rollback segment.
I try to drop the tablespace with the following commands:   startup mount
  alter tablespace datafile 'datafile_name' offline drop;   alter tablespace open;

all this fine, when the database was opened I try to drop the tablespace with the command :
  drop tablespace 'tablespace_name' including contents;

and I have the error message :
ORA-01548: active rollback segment 'RB_DATA' found,

           terminate dropping tablespace

It's nor online or offline.
I can't drop this rollback segment, his status is 'needs recovery' !!

I heard that I need to restart the database after adding a variable to the INIT.ORA file for the rollback segment...

Has anybody know what I must add at the init.ora file?

any help are very appreciated.
Haithem

   _______       ___________  __
   \      \     /          / / /             Haithem Abdelkefi
    \      \   /          / / /              Vigie Informatique 2000 Inc.
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