unable to dump database, toast errors

Greetings,
I'm running postgresql-7.2.1 on Redhat-7.2, and when attempting to
perform a dump with the command:
pg_dump -Ft -b -o DB_NAME > /tmp/db.tar

it chugs away for a few minutes, and then dies with the following error:

pg_dump: dumping out the contents of table artifact_file
pg_dump: ERROR: unexpected chunk number 0 (expected 1) for toast value
7685119
pg_dump: lost synchronization with server, resetting connection
pg_dump: SQL command to dump the contents of table "artifact_file"
failed: PQendcopy() failed.
pg_dump: Error message from server: pg_dump: The command was: COPY
"artifact_file" WITH OIDS TO stdout;
pg_dump: *** aborted because of error

I've tried running vacuumdb as follows:
vacuumdb -z -v -a -f

and its come up clean every time, so i'm really at a loss on how to
resolve this. If it matters, the artifact_file table has 782 rows, and
is comprised of text and integer datatype columns.

Any suggestions would be greatly appreciated. thanks!