No one parent tuple was found

Hi,

We are using postgresql 7.2.3 on redhat 7.1.

When we run vacuum full we get an error message 'No one parent tuple was
found'. But vacuum analyze goes fine. Infact 4 months back we had same
error while we were using 7.2.1. So we did upgrade to 7.2.3 and it went
off fine then. But now the same error crops up. What can be done in this
case? Googling and search in the archive doesn't help much.

regards,
bhuvaneswaran