It works!
Thank you very much

Moving to IMP queue, issue not specific to groupware bundle.

can you try the changes I just committed to CVS (link to diff in 
comment below)?

Changes have been made in CVS for this ticket:

Fix parameter passing to registry#call
Bug: 8726
http://cvs.horde.org/diff.php/imp/templates/prefs/sourceselect.inc?rt=horde&r1=1.21.10.4&r2=1.21.10.5&ty=u

I see these httpd errors when I enter on Address books Option for IMP:

[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, boolean given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
array_keys() expects parameter 1 to be array, null given in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 8, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, string given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, string given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, string given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, string given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:   
call_user_func_array() expects parameter 2 to be array, string given 
in /var/www/html/horde-webmail-1.2.4/lib/Horde/Registry.php on line 
630, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:  Invalid 
argument supplied for foreach() in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 74, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:  Invalid 
argument supplied for foreach() in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 74, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:  Invalid 
argument supplied for foreach() in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 74, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:  Invalid 
argument supplied for foreach() in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 74, referer: https://xx/services/prefs.php?app=imp
[Wed Nov 25 16:31:41 2009] [error] [client xx] PHP Warning:  Invalid 
argument supplied for foreach() in 
/var/www/html/horde-webmail-1.2.4/imp/templates/prefs/sourceselect.inc 
on line 74, referer: https://xx/services/prefs.php?app=imp

I can't reproduce this.

Any errors in either your horde log, server log, or javascript console?

I'm sure. I select an address book on right hand (a "selected" one). 
And the search field is always empty.

Are you sure you are clicking one of the *selected* address books (in 
the right hand column) and not one of the unselected address books? 
The field list will only show when one of the address books in the 
selected column are highlighted.

I have horde-webmail with shared address books and this turba sources.php:

$cfgSources['localsql'] = array(
...
         'firstname' => 'object_firstname',
         'lastname' => 'object_lastname',
         'middlenames' => 'object_middlenames',
         'namePrefix' => 'object_nameprefix',
         'nameSuffix' => 'object_namesuffix',
         'name' => array('fields' => array('namePrefix', 'firstname',
                                           'middlenames', 'lastname',
                                           'nameSuffix'),
                         'format' => '%s %s %s %s %s',
                         'parse' => array(
                             array('fields' => array('firstname', 
'middlenames',
                                                     'lastname'),
                                   'format' => '%s %s %s'),
                             array('fields' => array('firstname', 'lastname'),
                                   'format' => '%s %s'))),
         'email' => 'object_email',
...
     'search' => array(
         'name',
         'email'
     ),
     'strict' => array(
         'object_id',
         'owner_id',
         'object_type',
     ),
     'export' => true,
     'browse' => true,
     'use_shares' => true,
     'list_name_field' => 'lastname',
);

In IMP prefs I set
$_prefs['search_sources'] = array(
     'value' => '',
     'hook' => true,
     'locked' => false,
     'shared' => true,
     'type' => 'implicit');

$_prefs['search_fields'] = array(
     'value' =>  '',
     'locked' => false,
     'shared' => true,
     'type' => 'implicit');

It works. From IMP Option --> Address book I see in the right box (seleceted
address books) my shared address books. Autocomplete works with default fields
(name).

But the box:

"Click on one of your selected address books and then select all fields
to search.
To select multiple fields, hold down the Control (PC) or Command (Mac)
while clicking."

is always empty. No fields shown, same for all address books. I can't set my
personal "search_fields" values.

Regards