pg_autovacuum is not working

Hi list
This is my first post here, and I've searched google but couldn't find the
solution.

I'm trying to run pg_autovacuum on all my databases. All my Debian sarge
machines use version 7.4.5-3
postgresql install
postgresql-client install
postgresql-contrib install
postgresql-dev install
postgresql-doc install

postgres.conf options are
stats_start_collector = true
stats_row_level = true

postmaster.conf options are
AUTOVACUUM=yes
AVAC_LOG=/var/log/postgresql/autovacuum_log

pg_hba.conf options are
local all postgres ident sameuser
local all all ident sameuser

restart postgresql gives this message in the logs:

autovacuum.log
[2004-10-29 12:41:20 PM] Error: GUC variable stats_row_level must be enabled.
[2004-10-29 12:41:20 PM] Please fix the problems and try again.

postgres.log
2004-10-29 12:48:58 [29677] LOG: unexpected EOF on client connection

What could be the reason for this. I have a test machine with the exact same
options and databases as the production servers and it works find there. But
on ~15 production servers I can't get rid of this message.
I can provide strace of pg_autovacuum, but I didn't find many usefull
information in it.

Please advice
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