vacuum is failing

I've got a server running PostgreSQL-7.2.3 on RHAS-2.1. The version
of Postgresql is *not* my choice, I would have gone with something
much more current, but i digress.

Running 'vacuumdb -a -z -v -f' has started failing:

NOTICE: Index pg_toast_218644531_idx: Pages 1; Tuples 0.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
NOTICE: Analyzing doc2_review_comments
NOTICE: --Relation groups--
NOTICE: Pages 28: Changed 0, reaped 2, Empty 0, New 0; Tup 331: Vac
2, Keep/VTL 0/0, UnUsed 1, MinLen 160, MaxLen 1988; Re-using:
Free/Avail. Space 13360/12448; EndEmpty/Avail. Pages 0/17.
CPU 0.01s/0.00u sec elapsed 0.07 sec.
NOTICE: Index grps: Pages 2; Tuples 331: Deleted 2.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
NOTICE: Index groups_public: Pages 2; Tuples 331: Deleted 2.
CPU 0.00s/0.00u sec elapsed 0.02 sec.
NOTICE: Index groups_status: Pages 2; Tuples 331: Deleted 2.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
NOTICE: Index groups_type: Pages 2; Tuples 331: Deleted 2.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
NOTICE: Index group_unix_uniq: Pages 4; Tuples 331: Deleted 2.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
ERROR: No one parent tuple was found

Anyone have any suggestions on how to correct this? This DB serves a
web based PHP application, and right now there isn't any end user
noticable problems, and i'd like to keep it that way :)

thanks in advance!

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L. Friedman netllama(at)gmail(dot)com
LlamaLand http://netllama.linux-sxs.org