Aborted Transaction During Vacuum

I've been getting a strange error from the vacuum command. When I try
'vacuum verbose analyze' the vacuum goes through the tables fine until
just after finishing one particular table. Then I get the error:

NOTICE: AbortTransaction and not in in-progress state
pqReadData() -- backend closed the channel unexpectedly.       This probably means the backend terminated abnormally
  before or while processing the request.
 
We have lost the connection to the backend, so further processing is
impossible. Terminating.


When I try to vacuum the tables individually, I get no problems with
aborted backends.

Does anyone know what is going on here?

-Tony

PostgreSQL 6.5.1 on RH Linux 6.0, PII/400 MHz, 512 Meg RAM, 18 Gig HD