Oracle 11g r2: Cannot create partition on timestamp field

I have data with a timestamp field of the form ’2014-01-01 00:00:00.99′ in one of the columns. I want to create a new partition for the table every month. For this I did something like this.

CREATE TABLE t (id NUMBER , tstamp timestamp )
  PARTITION BY RANGE (tstamp)  (
    PARTITION t_jan_2009 VALUES LESS THAN (to_timestamp('2009-02-01 00:00:00.00','YYYY-MM-DD HH24:MI:SS.FF2')),
    PARTITION t_feb_2009 VALUES LESS THAN (to_timestamp('2009-03-01 00:00:00.00','YYYY-MM-DD HH24:MI:SS.FF2'))
);  

INSERT INTO t SELECT 1, '2009-02-10 12:34:45.56' from dual;

This is not the actual data but an equivalent sample. It gives the same error.
SQL Error: ORA-01843: not a valid month

Why am I getting this error? Do I need to do something more?