Error: missing chunk number ...

Hi,

I've recently observed some strange behavior using postgresql 7.2.1 on a
RH-7.3 system. I've got a service for fetching rss feeds from the web.
These feeds are stored into a text column. Here's how the table looks like:

Column | Type | Modifiers
------------------+--------------------------+-----------
channel_id | integer |
dataurl | character varying(1000) |
...
...
latest_feed | text |
feedidx | txtidx |
Indexes: hellofeedidx

(feedidx uses tsearch and indexes the faulty column, namely latest_feed).

This is not on a production system. After running this service for a
while (almost a week). I get messages like:

# select * from rss_channels;
ERROR: missing chunk number 1 for toast value 797979

If I try to delete the culprit row. I get:
# delete from rss_channels where channel_id=116;
ERROR: simple_heap_delete: tuple already updated by self

I'm running a full vacuum daily:
su - postgres -c 'vacuumdb --full --analyze --quiet --all'

and a simple vacuum once every hour:
su - postgres -c 'vacuumdb --analyze --quiet --all'

Here's how I configure and run PG:
./configure --enable-multibyte=UNICODE --with-tcl --with-perl
--enable-syslog

su -l postgres -c 'export LANG=C; /usr/local/pgsql/bin/postmaster -N 200
-B 1000 -o "-S 2000" -S -D /usr/local/pgsql/data '

Note that I cannot do a pg_dump on the rss_channels table.

Any idea of what might be the problem?

Best wishes,
Neophytos