pg_class corrupted ?

Hi all,

After a severe HD crash and the impossibility to read old DAT with our
new DAT drive, I've been able to copy $PGDATA/base/mabase on a new HD.
I've found all the tables data, and even the java intranet based on it
is working fine.

My problem is that when I tried to make a dump of the copied DB for a
new backup I've had the following error :
pg_dump: query to obtain list of tables failed: ERROR: Relation
pg_class does not have attribute 1

I can run psql but \dt causes this error :
ERROR: Relation pg_class does not have attribute 3

I can make a select * from pg_class but when I select a column from it
(i.e. 'select relname from pg_class'), I have the error again :
ERROR: Relation pg_class does not have attribute 1.

As I'm not a specialist, I can't find a solution or workaround for this
problem, I've not been able to find a solution on the net or forums.
Anybody has an idea ?

Thanks.

Bruno Thomas

PS: postresql version is 7.2.1