FlushRelationBuffers returned -2

I noticed my nightly vacuum process has started dying on a certain relation
last night. When I try to vaccum verbose it, I get the following output.

I can still do "SELECT * FROM filelist".

filelist is a table which has 12146 rows in it, with some 15 columns. Two
fields in approx 8-9000 of these rows are updated each night. No other
activity in the database while I vacuum (nobody even connected).

Restarting the postmaster corrected the problem.

Database is version 7.0.2 running on Linux 2.2.16/libc5. Started with
parameter "-B 512".

//Magnus



NOTICE:  --Relation filelist--
NOTICE:  Pages 847: Changed 0, reaped 821, Empty 0, New 0; Tup 12146: Vac
10733, Keep/VTL 0/0, Crash 0, UnUsed 11548, MinLen 92, MaxLen 1165;
Re-using: Free/Avail. Space 4329756/5420; EndEmpty/Avail. Pages 537/50. CPU
0.36s/0.09u sec.
NOTICE:  Index filelist_date_index: Pages 129; Tuples 12146: Deleted 0. CPU
0.04s/0.12u sec.
NOTICE:  Index filelist_dirid_index: Pages 134; Tuples 12146: Deleted 0. CPU
0.03s/0.18u sec.
NOTICE:  Index filelist_id_index: Pages 129; Tuples 12146: Deleted 0. CPU
0.06s/0.16u sec.
NOTICE:  Index filelist_name_index: Pages 247; Tuples 12146: Deleted 0. CPU
0.17s/0.15u sec.
NOTICE:  Rel filelist: Pages: 847 --> 310; Tuple(s) moved: 0. CPU
0.10s/0.07u sec.
NOTICE:  FlushRelationBuffers(filelist, 310): block 0 is referenced (private
0, global 5)
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.