Oracle Database Discussions

I have created a range partitioned table in Oracle 11G. While trying to add partition its showing an error.

-- Create table
create table TEST_COUNTER
(
CIKEY INTEGER not null,
LAST_COUNT_ID INTEGER,
LAST_EVENT_ID INTEGER,
LAST_DETAIL_ID INTEGER,
CI_PARTITION_DATE TIMESTAMP(6)
)
partition by range (CI_PARTITION_DATE)
(
partition P_TEST_COUNTER_120930 values less than (TIMESTAMP' 2012-09-30 00:00:00')
tablespace SOASIT2_SOAINFRA_TBS
pctfree 10
initrans 1
maxtrans 255
storage
(
initial 64K
next 1M
minextents 1
maxextents unlimited
),
partition P_TEST_COUNTER_121007 values less than (TIMESTAMP' 2012-10-07 00:00:00')
tablespace SOASIT2_SOAINFRA_TBS
pctfree 10
initrans 1
maxtrans 255
storage
(
initial 64K
next 1M
minextents 1
maxextents unlimited
);

alter table test_counter add partition P_TEST_COUNTER_121014 VALUE LESS THAN (TO_DATE('2012-10-14 00:00:00','YYYY-MM-DD HH24:MI:SS'));

Error : ORA-14020: this physical attribute may not be specified for a table partition

I have tried with varies date conversion formats but error is the same. Could anyone plz help me to resolve this issue.