postgres catalog files problem

Hi,
I noticed that I have too many records in my pg_ catalog files with the same name. For example
if I give this query, which checks for the triggers that do not have corresponding tables in the pg_class

select * from pg_trigger where tgrelid not in (select relfilenode from pg_class),

I get  set of records like this (omitted some fields)

tgrelid                 tgname                                   tgfoid     tgtype          tgconstrname
629324      RI_ConstraintTrigger_654082              1644       5          payment_fk_id      ...                                                                                                                                
 629324      RI_ConstraintTrigger_654083              1645       17        payment_fk_id    ...
........

That is there are records in my pg_trigger that has no corresponding tgrelid in pg_class. Why is that? Is it okay to manually delete these records from the catalog files?

So Im getting this errorthis error when I try to update some tables
' could not open relation with oid'

Thanks for your help
josh