Changes have been made in Git for this ticket:

Fix checking of return value from ldap_exists() (Bug #9235).

http://git.horde.org/diff.php/framework/Group/lib/Horde/Group/Ldap.php?rt=horde-git&r1=e88d86628e59710a0c3396b5712b4f98638269f1&r2=902b4483b0b40da51a1116905a8fdb46c0c4eb02

Having horde configured to work with groups and having a 
calendar/contact list shared with a group caused the following error 
when accessing turba/kronolith:

"Internal Error: An attribute must ALWAYS match itself:"

Transcript of chat with Jan Schneider
------------
[10/09/07 10:30:56] hi jan
[10/09/07 10:30:56] Joao Santos: I'm having a couple of problems with 
turba/kronolith
[10/09/07 10:31:22] Joao Santos: was wondering if you could give me some help?
[10/09/07 11:28:56] Jan Schneider: hi joao. shoot
[10/09/07 11:30:13] Joao Santos: well, i sahred calendar with a group
[10/09/07 11:30:33] Joao Santos: and then when I login and try to 
access the calendar i get the error
[10/09/07 11:30:33] Joao Santos: Ocorreu um erro fatal

Internal Error: An attribute must ALWAYS match itself:

Os detalhes foram enviados para o administrador do sistema.
[10/09/07 11:30:53] Joao Santos: this happens with both turba and kronolith
[10/09/07 11:31:49] Joao Santos: i've updated the version and 
reinstalled everythin, but keep bumping on this
[10/09/07 11:33:24] Jan Schneider: never heard of that error message before
[10/09/07 11:34:18] Jan Schneider: this seems to be coming from the 
ldap group driver
[10/09/07 11:34:49] Joao Santos: how can i try to debug this?
[10/09/07 11:36:03] Jan Schneider: the error is thrown in 
Horde_Group_Ldap#exists()
[10/09/07 11:36:30] Jan Schneider: i'm not sure what ldap_compare is 
supposed to do, but i'd start looking there
[10/09/07 11:52:24] Joao Santos: well aparently he tries to see if the 
group exists in the system
[10/09/07 11:52:30] Joao Santos: but doesn't find it
[10/09/07 11:53:35] Joao Santos: is ldap_compare a function of the 
horde ldap lib or from ldap itself?
[10/09/07 11:55:09] Joao Santos: I find it strange that internally the 
gid stored in the var gid is "cn"
[10/09/07 12:27:28] Jan Schneider: i think the logic in exists() is wrong
[10/09/07 12:27:55] Jan Schneider: the code and comments assume that 
-1 means "doesn't exist" and false means error
[10/09/07 12:28:00] Jan Schneider: but the php docs say the opposite
[10/09/07 12:28:37] Jan Schneider: and the error message in exists() 
is misleading at best
[10/09/07 12:29:05] Jan Schneider: try changing the "if ($res === 
false)" to "if ($res === -1)"
[10/09/07 13:35:56] Joao Santos: jan, that's exactly right