[horde] About the error "There was an error in the configuration form. Perhaps you left out a required field."

[Jason Wang]

Why I can’t Generate Horde Configuration?

OS : CentOS 5.0 + cyrus-sasl-2.1.22 + postfix-2.4.5 + dovecot-1.0.7
Database : postgreSQL-8.2.5
httpd : Apache2.2.6
PHP : php-5.2.4

My imap server use postgreSQL to authentication, I edit the dovecot-sql.conf as following:
  connect = host=localhost dbname=horde user=postgres password=postgres_pass
  password_query = SELECT user_uid as user, user_pass as password, user_uid as userdb_home, 1004 as userdb_uid, 1004 as userdb_gid FROM horde_users WHERE user_uid = '%u'
  user_query = SELECT user_uid as home, 1004 as uid, 1004 as gid FROM horde_users WHERE userid = '%u'

After install is over, I login to the horde initial setup page successfully and  when I click "Generate Horde Configuration", the system respond me: "There was an error in the configuration form. Perhaps you left out a required field." 
  But I check every tab and no any asterisk textbox empty.

And at the "users" module, it shows me: "Your authentication backend does not support adding users. If you wish to use Horde to administer user accounts, you must use a different authentication backend."
Which authentication backend will be supported? 
Now at the setup page's Authentication tab: my authenticating users backend is "Let a Horde application handle authentication" and The application is "imp".


Thank you very much for your kind support.
  Best Regards.

Jason Wang
E-mail : wjs at sha-etech.com