SQL & PL/SQL

Hi guys

I created the following table.

CREATE TABLE proj_task_details (task_id NUMBER(10) PRIMARY KEY NOT NULL,
                                                    based_on number(10),
                                                    task_in_charge VARCHAR2(30),
                                                    task_start_date DATE,
                                                    task_end_date DATE
                                                    );

The default NLS DATE FORMAT is

PARAMETER                      VALUE                                 

------------------------------ ----------------------------------------

NLS_DATE_FORMAT                DD-MON-RR

I am trying to insert the below row.

INSERT INTO proj_task_details (task_id, based_on, task_in_charge, task_start_date, task_end_date)
values ('02', '01','KOCHAR', '13-SEP-07', '14-SEP-07');

It throws the below error.

INSERT INTO proj_task_details (task_id, based_on, task_in_charge, task_start_date, task_end_date)

values ('02', '01','KOCHAR', '13-SEP-07', '14-SEP-07')

Error report -

SQL Error: ORA-01843: not a valid month

01843. 00000 -  "not a valid month"

*Cause:   

*Action:

I do not understand why it cant take month in the "SEP" format?