Again about temporary table

Couple a weeks ago (19.08.03 Subject: Temporaty tables) I've posted message
with question about errors I'm getting while using create temporaty table
command.
So I'm start digging in src code as Tom Lane did and found about 4 places
where such kind pf errors could happend

PostgreSQL 7.3.3

src/backend/catalog/dependency.c : 1621
src/backend/catalog/heap.c : 1663
src/backend/catalog/pg_constraint.c : 445
src/backend/utils/adt/ruleutils.c : 3125

As I see all this errors depend on HeapTupleIsValid() function return code.
If it's false then error happend.

In
1)  src/backend/utils/adt/ruleutils.c : 3125 HeapTupleIsValid() function is
used in generate_relation_name(Oid relid), which is as I understand
resposible to convert relid identificator into relation name
2) src/backend/catalog/dependency.c : 1621 HeapTupleIsValid() function is
used in getRelationDescription(StringInfo buffer, Oid relid) function, which
is getting relation description while specify relid.
3) src/backend/catalog/heap.c : 1663 HeapTupleIsValid() function is used in
SetRelationNumChecks(Relation rel, int numchecks) function. I don't realy
understand the meaning of that function
4) src/backend/catalog/pg_constraint.c : 445 HeapTupleIsValid() function is
used in RemoveConstraintById(Oid conId) which is responsible for   delete a
single constraint record.

So any ideas why I'm getting errors like:
Warning: pg_exec() [function.pg-exec]: Query failed: ERROR: cache lookup of
relation 149064743 failed . in table.php on line 169
The query on line 169 is :

CREATE TEMP TABLE tmp_table1 AS SELECT advert.time_create, (SELECT
employer.fullname FROM employer WHERE advert.empid=employer.id) as emp_name,
(CASE WHEN advert.status1 = 'A' THEN advert.postname1 ELSE advert.postname2
END) as postname, advert.enddate, advert.id as id FROM good_adv as advert

And right ahead

Warning: pg_exec()[function.pg-exec]:Query failed: ERROR: Relation
"tmp_table1" does not exist.

On query like :

SELECT * FROM tmp_table1