vacuum failure...

I've got a problem vacuuming a table and can't seem to find a way to 
fix it...

vacuum full verbose analyze folders;
NOTICE:  --Relation folders--
NOTICE:  Pages 18598: Changed 0, reaped 18598, Empty 0, New 0; Tup 
69849: Vac 0, Keep/VTL 0/0, UnUsed 1870572, MinLen 64, MaxLen 88; Re-
using: Free/Avail. Space 139159408/139159408; EndEmpty/Avail. Pages 
0/18598.       CPU 0.34s/0.09u sec elapsed 0.51 sec.
ERROR:  No one parent tuple was found

-Michael
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