Errors on VACUUM

I received the following error from a VACUUM ANALYZE:

NOTICE: FlushRelationBuffers(place, 454): block 231 is referenced
(private 0, global 4)
FATAL 1: VACUUM (vc_repair_frag): FlushRelationBuffers returned -2

and psql lost the connection right after that. This was repeatable,
after the first occurrence I re-started the postmaster and tried again,
same result. The particular table in question is static data, that is
it was originally filled in once by COPY and there were no subsequent
inserts or deletes. But I had just added a column to the table and
updated it from another table to eliminate a frequently-done join, that
was the reason for doing the VACUUM.

Since I had the text file with the complete table contents from the
original COPY, I decided to re-build the table, so next I did DROP
TABLE, and I got this:

NOTICE: Buffer Leak: [004] (freeNext=-3, freePrev=-3,
relname=place_pid, blockNum=1, flags=0xc, refcount=2 -1)
NOTICE: Buffer Leak: [005] (freeNext=-3, freePrev=-3, relname=place,
blockNum=231, flags=0xc, refcount=4 -1)
NOTICE: Buffer Leak: [008] (freeNext=-3, freePrev=-3, relname=place,
blockNum=85, flags=0xc, refcount=3 -1)
NOTICE: Buffer Leak: [011] (freeNext=-3, freePrev=-3, relname=place,
blockNum=0, flags=0xc, refcount=2 -1)
.
.

repeating about 20 more times with blockNum varying, and finally ending
with the table being dropped. I then re-built the table from scratch
and everything seems to be fine now, VACUUM no longer gives errors.

Here is my system configuration:

PostgreSQL 7.0.2
RedHat Linux 7.0
P-III 800, 768MB RAM, 80GB disk

So I'm wondering what happened here, what might have caused the original
error, if something else is potentially still corrupted, and if I should
maybe re-build the whole database to be safe?

Advice much appreciated!

Bob Smith
Hammett & Edison, Inc.
bsmith(at)h-e(dot)com