heap_mark4update: (am)invalid tid

Hi,

I am using 7.3.2 on redhat linux 7.3.

I am getting this error during update. My update sql is,

test_pg=# update po_header set emp_name = a.user_name from users a where
emp_code = a.user_code and emp_name != a.user_name and a.user_name is not
null;

I referred the link,
http://archives.postgresql.org/pgsql-bugs/2003-04/msg00076.php .

My answers are,

(a) yes, i have before triggers
(b) no, users table donot have multi entries

Should i require to upgrade? or, Is there any smart sql?

TIA.

regards,
bhuvaneswaran

Table definitions:
Table "public.po_header"
Column | Type | Modifiers
---------------------+--------------------------+--------------------------------
po_no | text |
seq_x | integer |
seq_y | integer |
comp_code | text |
generated_by | text |
supp_code | text |
emp_code | text |
....
emp_name | text |
...
Indexes: po_header_uniq_idx unique btree (po_no, comp_code, seq_x, seq_y),
...
Check constraints: "po_header_type" ((("type" = 'NEW'::text) OR ("type" = 'CHANGED'::text)) OR ("type" = 'CANCELLED'::text))
Triggers: RI_ConstraintTrigger_17175491,
...
tapproval_date,
tbuyer_supp_map,
texception,
tmtime_po_header,
tnames_po_header,
tpo_flags_insert,
tprocess_complete,
tref_supplier,
tstatus_count

Table "public.users"
Column | Type | Modifiers
-------------------+--------------------------+-----------------------------------------------
user_id | integer | not null default nextval('user_id_seq'::text)
login_id | text |
user_code | text |
comp_code | text |
user_name | text |
...
Indexes: users_pkey primary key btree (user_id),
...
Check constraints: "users_email_id" ((email_id ~ '@'::text) AND (email_id ~ '.'::text))
Triggers: RI_ConstraintTrigger_17175378,
...
tmtime_users