table disappear from pg_class

Hi all,
I have a problem with a table which is disappeared from pg_class
with all objects related (views, indexes and so on).
pg_dump against this table does not work (I think because it is not
present in pg_class).

The strange behaviour is that I can select data from this table !!
We are using a 7.4.6 on linux (slackware).

Any help will be appreciated we are in emergency

regards
M.