[horde] Carddav not showing contacts

[pillul]

Hey Guys,

i have a bigger problem with useing carddav.
I'd like to share one global adressbook for all our employees but cant get  
the sync work.
After adding a adressbook and assigning some rights other users in the  
webmailer can see and use the book.

But when i try to add a carrdav client (mostly iOS) i can't get it work.
In the logs i can see that it tries to auth and has success:

2013-07-15T12:26:48+00:00 NOTICE: HORDE [imp] Login success for  
user at domain.de (Horde user user at domain.de) [4.5.6.7] to {0.1.2.3:993  
[imap]} [pid 5630 on line 157 of "/htdocs/mail/imp/lib/Auth.php"]

On the Iphone i see under "groups" my calendars but no contacts are  
showing up.
What can i do to debug or fix the problem?

Thank you!