Postgresql crash- any ideas?

Postgresql just reset itself, this is what I found in the log.

FATAL:  block 26 of 1663/17228/3425958479 is still referenced (local 2)
LOG:  server process (PID 1887) exited with exit code 1
LOG:  terminating any other active server processes

There wasn't much activity in the database at the time.  A vacuum on the entire database finished 5 minutes before this
errorand a vacuum of pg_attribute was in-progresss.   re-vacuuming pg_attribute was ok. 

pg version: 8 beta3

I only found this reference so far:
http://archives.postgresql.org/pgsql-bugs/2004-09/msg00029.php

-michael