Rodrigo Gonzalez <rjgonzale(at)gmail(dot)com> writes:
> PgSQL is returning that error when I open pgdmin and when I run some
> queries related to pg_buffercache. Also pg_dump cannot dump the DB.
> PgSQL version is 8.3.3 and happened one day after loading the DB there.
That raises a lot of questions about the trustworthiness of the platform
you're using (hardware, kernel, etc). In 8.3, 2836 is pg_proc's TOAST
table and should certainly never get deleted. I think you have
filesystem or hardware issues.
regards, tom lane