alter table A: relation <unknown table not A > error

Hi every one,

i'm having a trouble with an alteration( add a column ) to a table.

When i issue a update table A add ... the result is

ERROR: relation <strange table> not found.

Right now i'm running PostgreSQL 7.2.1, but the database has been migrated
from PostgreSQL 7.1 via an SQL dump.
The mysterious table has existed on my database( on pg 7.1 ) as a
temporary table...after that i have just dopped the table.
I have searched every references on pg_class and pg_triggers to this
mysterious table, but i haven't found anything.
Is there any way of vaerifying the logical integrity of the catalog
tables( pg_* )?
Does any one have a clue for this?

Thank's
Miguel Carvalho