Insert into table error - ora-01722 invalid number

Question

Need some assistance with inserting data into a table. The date column keeps on failing to insert.
here is my insert statement
insert into tab_mod_history (TABLE_OWNER, TABLE_NAME, PARTITION_NAME, SUBPARTITION_NAME, INSERTS, UPDATES, DELETES, TIMESTAMP, TRUNCATED)
values ('$i_owner','$i_table','$i_part_name','$i_subpart_name','$i_ins','$i_upd','$i_del','$time','$trunc');Script loads data for partition tables, but not normal tables with the timestamp column
I select the data using this select statement:
select table_owner, table_name, partition_name, subpartition_name, inserts, updates, deletes, timestamp, truncated
from dba_tab_modifications
where table_owner in ('scott','MAC')
order by table_name;

Answer 1

ok here are the errors:
values ('MAC','WC_MST','11','1','1','12/04/2011','NO','','')
ERROR at line 2:
ORA-01722: invalid number
Session altered.
values ('MAC','WF_05A','208','128','208','18/02/2011','NO','','')
ERROR at line 2:
ORA-01722: invalid numberHere is the table structure
SQL> desc tab_mod_history
Name                                      Null?    Type
TABLE_OWNER                                        VARCHAR2(30)
TABLE_NAME                                         VARCHAR2(30)
PARTITION_NAME                                     VARCHAR2(30)
SUBPARTITION_NAME                                  VARCHAR2(30)
INSERTS                                            NUMBER
UPDATES                                            NUMBER
DELETES                                            NUMBER
TIMESTAMP                                          DATE
TRUNCATED                                          VARCHAR2(3)
DROP_SEGMENTS                                      NUMBERI used the column names to create the variables..that is why $time was used.
How else could I have done it????
thought this was easy..but to my dismay...