ORA-30040

Problem:
I have taken the undo tablespace offline through spfile. I shutdown the database and start the db next day from pfile

"IT GIVE ME THE SYSTEM ERROR, DISCONNECTION FORCED"

I tried to start database in nomount stage (it works)
alter database mount (it works)

But when I issue

alter database open OR simply type the "startup" command it gives the below error

Errors in file d:\sam\udump\sam_ora_3700.trc:
ORA-30040: Undo tablespace is offline

Thu Jan 22 00:00:10 2009
Error 30040 happened during db open, shutting down database
USER: terminating instance due to error 30040
Instance terminated by USER, pid = 3700
ORA-1092 signalled during: alter database open...

Solution:
Check UNDO_TABLESPACE (must be set to ur undo tablespace name) and UNDO_MANAGEMENT (set it to AUTO) parameters in PFILE or SPFILE