vacuumdb problem

Hi!
I have a problem with vacuumdb on one of my tables.

(spiral:3)-[~]$vacuumdb -t osoby -v dziekanat
NOTICE: --Relation osoby--
NOTICE: Pages 229: Changed 0, reaped 16, Empty 0, New 0; Tup 4427: Vac 5,
Keep/VTL 0/0, Crash 0, UnUsed 70, MinLen 64, MaxLen
616; Re-using: Free/Avail. Space 18176/2288; EndEmpty/Avail. Pages
1/10. CPU 0.02s/0.00u sec.
NOTICE: Index osoby_Imię_key: Pages 44; Tuples 4427: Deleted 0. CPU
0.01s/0.01u sec.
NOTICE: Index osoby_pkey: Pages 15; Tuples 4427: Deleted 0. CPU
0.00s/0.00u sec.
NOTICE: Rel osoby: Pages: 229 --> 228; Tuple(s) moved: 0. CPU 0.01s/0.00u
sec.
NOTICE: FlushRelationBuffers(osoby, 228): block 223 is referenced
(private 0, global 1)
FATAL 1: VACUUM (vc_repair_frag): FlushRelationBuffers returned -2
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
connection to server was lost
vacuumdb: vacuum failed

this table is referenced in my db by a tree of FOREIGN KEYs.

however my db seems to work and I am able to do pg_dump
Rescently, I dumped and restored it and for a few days I was able to
do vacuumdb. Today, the problem is here again.

any ideas?

thanks for any help.

(I use Postgres ver 7.0.2 on Debian Potato/ dual PII box)