Postgres Database Corrupted

Hi,

I don't know how my database got corrupted. Whenever I try taking
pg_dump, I get the following error:
getTypes(): SELECT failed. Explanation from backend: 'ERROR: pg_user:
Table does not exist.

There are so much amount of data. I use postgres 6.5 version. Please
tell me how to rectify this.



Regards,
Venkat