ok, i found this:
'category' => 'object_category',

in my backends.local.php (it wa copied from older version). i removed 
it and it's working now, thank you.

Yes, I'm sure. object_category only exists in the database migrations:

mrubinsk@coffee:turba (FRAMEWORK_5_2)$ grep -r object_category ./
.//migration/10_turba_upgrade_categoriestotags.php:            $sql = 
'SELECT object_uid, object_category, owner_id FROM turba_objects';
.//migration/10_turba_upgrade_categoriestotags.php:                     
     $row['object_category']
.//migration/10_turba_upgrade_categoriestotags.php:         
$this->removeColumn('turba_objects', 'object_category');
.//migration/10_turba_upgrade_categoriestotags.php:         
$this->addColumn('turba_objects', 'object_category', 'string', 
array('limit' => 80));
.//migration/10_turba_upgrade_categoriestotags.php:        $sql = 
'UPDATE turba_objects SET object_category = ? WHERE object_uid = ?';
.//migration/1_turba_base_tables.php:             
$t->column('object_category', 'string', array('limit' => 80));

are you sure? see the attachment, i'm running newest unstable turba.

That query doesn't exist in current Turba.

This is in error log:

WARN: HORDE [turba] PHP ERROR: mysqli::real_escape_string() expects 
parameter 1 to be string, array given [pid 13081 on line 188 of 
"/usr/share/php/Horde/Db/Adapter/Mysqli.php"]

ERR: HORDE [turba] SQL QUERY FAILED: Unknown column 'object_category' 
in 'field list'
         INSERT INTO turba_objects (object_type, object_firstname,
           object_lastname, object_middlenames, object_nameprefix,
           object_namesuffix, object_alias, object_bday, object_spouse,
           object_anniversary, object_yomifirstname, object_yomilastname,
           object_photo, object_homestreet, object_homepob, object_homecity,
           object_homeprovince, object_homepostalcode, object_homecountry,
           object_workstreet, object_workpob, object_workcity,
           object_workprovince, object_workpostalcode, object_workcountry,
           object_otherstreet, object_otherpob, object_othercity,
           object_otherprovince, object_otherpostalcode, object_othercountry,
           object_tz, object_email, object_homephone, object_homephone2,
           object_workphone, object_workphone2, object_carphone,
           object_radiophone, object_companyphone, object_assistantphone,
           object_homefax, object_cellphone, object_fax, object_pager,
           object_imaddress, object_imaddress2, object_imaddress3, 
object_title,
           object_role, object_company, object_department, object_logo,
           object_assistant, object_manager, object_category, object_notes,
           object_url, object_freebusyurl, object_pgppublickey,
           object_smimepublickey, owner_id, object_uid, object_id) VALUES
           ('Object', 'it', 'test', '', '', '', '', NULL, '', NULL, '', '',
           NULL, '', '', '', '', '', '', '', '', '', '', '', '', '', 
'', '', '',
           '', '', '', 'test@example.com', '', '', '', '', '', '', '', 
'', '', '', '',
           '', '', '', '', '', '', '', '', NULL, '', '', '', '', '', 
'', '', '',
           'test@example.com',
           'censored',
           'censored2') [pid 13081 on line 315 of 
"/usr/share/php/Horde/Db/Adapter/Mysqli.php"]