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
anexplicit 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
anexplicit cast
 

what could be the problem here?

Thankx in advance

With Regards,
Bhuvaneswar.