Originally posted by davey23uk
create a tablespace called undo or something and set this to be your undo tablespace in your init.ora file
Additionally..
You will have to set these two parameters in init.ora

Code:
UNDO_MANAGEMENT = AUTO
UNDO_TABLESPACE = your_undo_tbs
To create UNDO tablespace see the syntax "CREATE UNDO TABLESPACE.."

HTH