Strange Problem As Type Casting

hi all,

i am using postgresql 7.1.
here i am facing some strange problem for last 2 days.

i have a table 'users' as below

test=> \d users
Table "users"
Attribute | Type | Modifier
-------------------+--------------------------+-----------------------------------------------
user_id | integer | not null default nextval('user_id_seq'::text)
login_id | text |
user_code | text |
comp_code | text |
user_name | text |
password | text |
last_login | timestamp with time zone |
noof_logins | integer |
dob | date |
eff_date | date |
is_active | boolean | default 'f'
email_id | text |
creation_time | timestamp with time zone |
modification_time | timestamp with time zone |
Indices: users_login_id_key,
users_pkey,
users_user_code_key
Constraint: ((email_id ~ '@'::text) AND (email_id ~ '.'::text))

----

here user_id is of type integer and not serial. ie.. i explicitly created
the sequence and had it as default.
while i update user_id field

test=> UPDATE users set user_id=1 ,login_id='admin' where user_id='1346';
ERROR: Unable to identify an operator '=' for types 'text' and 'int4'
You will have to retype this query using an explicit cast

again i tried it as below
test=> UPDATE users set login_id='admin' where user_id='1346';
UPDATE 1
test=> UPDATE users set user_id='1' where login_id='admin';
ERROR: Unable to identify an operator '=' for types 'text' and 'int4'
You will have to retype this query using an explicit cast

what could be the problem here?

Thankx in advance

With Regards,
Bhuvaneswar.