tuplestore: write failed

Hi All!
I'm working on postgres for the last 3 weeks. I'm trying to port several
applications from oracle to postgres. I load all the tables and now I'm
testing performance issues. Today, when I execute a very heavy query,
the query abort (no message on client) in about 20/30 minutes. In
server's logfile I found this:

2002-10-16 11:53:25 ERROR:  tuplestore: write failed

I run again the query an I get the same error.
I check the disk space... everithing ok.

I did several modifications on postgres.conf:
tcpip_socket = true
shared_buffers = 16384
wal_buffers = 16
sort_mem = 512
vacuum_mem = 16384
wal_files = 4 # range 0-64
checkpoint_segments = 3
fsync=false
enable_seqscan = true
enable_indexscan = true
enable_tidscan = true
enable_sort = true
enable_nestloop = true
enable_mergejoin = true
enable_hashjoin = true
geqo = true
geqo_selection_bias = 2.0
geqo_threshold = 11
geqo_pool_size = 0
geqo_effort = 1
geqo_generations = 0
geqo_random_seed = -1
stats_start_collector = true
stats_reset_on_server_start = true
stats_command_string = true


I create several indexes after data load, and then run vacuum -z.

But I can't find any references for this error!

If anybody can guide me...

thanks in advance

--
Fernando