[turba] Failed to access the specified address book

[Thomas Faust]

Hi turba-group.

I'm getting headache with the configuration from turba.
The configuration for one of the addressbooks looks like this:

$cfgSources['localsql'] = array(
    'title' => 'My Postgres Addressbook',
    'type' => 'sql',
    'params' => array(
        'phptype' => 'pgsql',
        'hostspec' => 'localhost',
        'username' => 'horde',
        'password' => 'pass',
        'database' => 'horde',
        'table' => 'turba_objects'
    ),

The PostgreSQL database is running.
The user 'postgres' is able to acces the database with: 'psql -d horde -U 
horde' and the table 'turba'object' is present:

              List of relations
 Schema |       Name       | Type  |  Owner
--------+------------------+-------+----------
 public | horde_categories | table | postgres
 public | horde_prefs      | table | postgres
 public | horde_users      | table | postgres
 public | turba_objects    | table | postgres
(4 rows)

When I try to browse this addressbook I'm getting the following message:

"Failed to access the specified address book."


What can cause this message? Which log-files can help me to solve this 
problem?
I'm sorry for my newby-questions, but appreciate any help.

Thomas