dovecot - Jun 2011 - I can't setup namespace per user (with settings keept in sql db)

Hello!
I'm trying to setup additional namespace. I'd like to have this setting
per user and keep it in postgresql.
Global namespace is defined in this way:
namespace {
  inbox = yes
  location   prefix   separator = .
}
(mail_location is getting from db)
I don't know how should looks like database field:(
Now i have such configuration:
user_query = select .... dovecot_location AS location, dovecot_namespace
AS namespace FROM ...

In db i have this:
# select dovecot_location, dovecot_namespace from exim_users where
dovecot_namespace is not null;
     dovecot_location      | dovecot_namespace
---------------------------+-------------------
 location="mdbox:~/.mdbox" | prefix="testn"
(1 row)

but this isn't good configuration. I've got in log:

debug: sql(marcin at mejor.pl,62.121.127.119): SELECT
'/dane/domeny/mejor.pl/mail/marcin/' as home, dovecot_typ_skrzynki
||':'|| '/dane/domeny/mejor.pl/mail/marcin/' ||'
.'|| dovecot_typ_skrzynki as mail_location,
'*:bytes='||quota_mb||'M' as
quota_rule , dovecot_location AS location, dovecot_namespace AS
namespace FROM exim_users WHE
RE login = lower('marcin') AND domena = lower('mejor.pl')
Debug: master out:
USER#0112138832897#011marcin at
mejor.pl#011home=/dane/domeny/mejor.pl/mail/marcin/#011mail_location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildi
r#011quota_rule=*:bytes=0M#011location=location="mdbox:~/.mdbox"#011namespace=prefix="testn"
Login: user=<marcin at mejor.pl>, method=CRAM-MD5, rip=62.121.127.119,
lip=193.238.12.139, mpid=17929, TLS
Debug: Loading modules from directory: /usr/lib/dovecot
Debug: Module loaded: /usr/lib/dovecot/lib10_quota_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib11_imap_quota_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib15_notify_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_autocreate_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_fts_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_mail_log_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib20_zlib_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib21_fts_squat_plugin.so
Debug: Module loaded: /usr/lib/dovecot/lib30_imap_zlib_plugin.so
Debug: Added userdb setting:
mail_location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: Added userdb setting: plugin/quota_rule=*:bytes=0M
Debug: Added userdb setting: plugin/location=location="mdbox:~/.mdbox"
Debug: Added userdb setting: namespace=prefix="testn"
Debug: Effective uid=8, gid=12, home=/dane/domeny/mejor.pl/mail/marcin/
Debug: Quota root: name=User quota backend=dict args=:proxy::quota
Debug: Quota rule: root=User quota mailbox=* bytes=0 messages=0
Debug: dict quota: user=marcin at mejor.pl, uri=proxy::quota, noenforcing=0
Debug: Namespace : type=private, prefix=, sep=., inbox=yes, hidden=no,
list=yes, subscriptions=yes
location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: maildir++: root=/dane/domeny/mejor.pl/mail/marcin/.maildir,
index=, control=, inbox=/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: Namespace : type=private, prefix=, sep=, inbox=no, hidden=no,
list=yes, subscriptions=yes
location=maildir:/dane/domeny/mejor.pl/mail/marcin/.maildir
Debug: maildir++: root=/dane/domeny/mejor.pl/mail/marcin/.maildir,
index=, control=, inboxError: user marcin at mejor.pl: Initialization failed:
namespace
configuration error: Duplicate namespace prefix: ""
Error: Invalid user settings. Refer to server log for more information.

I've got stuck, i don't have idea how configuration should looks:(
Thanks for any help!
dovceot-2.0.13