Tablespace Creation trouble --Help!

I hope this is an easy question:  

 I have just set up my first ORACLE db 7.3.2.0 on HP-UX 10.10 on a  9000/735. The database is created. I am trying to add tablespaces. I  used the following command to create a rollback segment first:  CREATE ROLLBACK SEGMENT rbs_1

         TABLESPACE SYSTEM
         STORAGE ( INITIAL 3
                   MINEXTENTS 121
                   MAXEXTENTS 10240
                   NEXT 10240
                   PCTINCREASE 0)
         OPTIMAL TO 250 K;
 

 I receive this error message:
CREATE ROLLBACK SEGMENT rbs_1
  *
  ORA-00406: COMPATIBLE parameter needs to be 7.3.0.0.0 or greater

Does anyone know what this error message signifies? I don't have a reference for SQL error messages yet, and I need to get this going for my developers. The same message appears for when I tried to create a TABLESPACE. ANY help is appeciated.

Thanks much,

Jason Berryhill

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