DELETE statement KILL backend <AGAIN>

Hello all,

I have a strange problem that I can't understand.
I have been my PostgreSQL-6.3.2 on Linux-ELF-2.0.34 working without any problem for many
months. This morning I can't DELETE anymore.
If I try to delete a row from any table I have this message:

PGexec() -- Request has sent to backend, but backend closed the
channel before responding.
This probably means the backend terminated abnormally before or while
processing the request.

and then the backend dies.

I tried every statement as:
INSERT
UPDATE
SELECT
DROP TABLE
and all of them works but DELETE,

I tried also VACUUM without success.

PLEASE help me !!

Best regards,
Jose' mailto:sferac(at)bo(dot)nettuno(dot)it