FATAL: could not read statistics message

We have been getting the following message in our log file since
upgrading to 8.0.3:

2005-07-20 21:24:15 BST [13299] FATAL:  could not read statistics
message: Resource temporarily unavailable

Does anyone know what this means?

The message seems to occur once every minute. We have the following
runtime statistics in our postgresql.conf

# - Statistics Monitoring -

#log_parser_stats = false
#log_planner_stats = false
#log_executor_stats = false
#log_statement_stats = false

# - Query/Index Statistics Collector -

#stats_start_collector = true
stats_command_string = true
#stats_block_level = false
#stats_row_level = false
#stats_reset_on_server_start = true

Also I notice that pg_stat_activity does not appear to refresh when I
query it to monitor current activity. I wonder if this is related?

Regards,

Alex Stanier.