Ich kann meine E-Mails nicht wie zuvor aufrufen, woran könnte dies liegen?
Das ganze Layout und Design hat sich verändert und ist sehr 
unübersichtlich geworden.

I'm afraid you need to track this down on your own.

After working with firefox for a while, I have noticed that the error 
is happening in all browsers that I have tested (IE, Chrome and 
Firefox).

If this is only happening with some browsers, find out what the 
difference is. Do the send different cookies? Do the cookie values 
change? Are there any POST parameters send or encoded differently?

I'm turning debug on to monitor and all I receive is this in the 
timestamp where the error appears:

2015-06-11T09:23:40-03:00 DEBUG: HORDE [imp] Load config file 
(conf.php; app: imp) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:40-03:00 DEBUG: HORDE [imp] Load config file 
(hooks.php; app: imp) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:40-03:00 DEBUG: HORDE [imp] Load config file 
(mime_drivers.php; app: horde) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:40-03:00 DEBUG: HORDE [imp] Load config file 
(mime_drivers.php; app: imp) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:41-03:00 EMERG: HORDE [imp] Invalid token! [pid 18428 
on line 540 of "/usr/share/pear/Horde/Session.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE 1. 
IMP_Contents_View->checkToken() /var/www/html/horde/imp/view.php:56
2. Horde_Session->checkToken() 
/var/www/html/horde/imp/lib/Contents/View.php:357

2015-06-11T09:23:41-03:00 DEBUG: HORDE [imp] Max memory usage: 9437184 
bytes [pid 18428 on line 608 of "/usr/share/pear/Horde/Registry.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [turba] Load config file 
(conf.php; app: turba) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [turba] Load config file 
(attributes.php; app: turba) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [turba] Load config file 
(backends.php; app: turba) [pid 18358 on line 109 of 
"/usr/share/pear/Horde/Registry/Loadconfig.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [turba] SQL  (0,0005s)
         SELECT object_id, object_type, owner_id, object_members,
           object_nameprefix, object_firstname, object_middlenames,
           object_lastname, object_namesuffix, object_email FROM turba_objects
           WHERE (object_email = 'dgrhcom@unicamp.br' OR owner_id = 'coutinho'
           AND ((LOWER(object_nameprefix) LIKE LOWER('%dgrhcom@unicamp.br%') OR
           LOWER(object_firstname) LIKE LOWER('%dgrhcom@unicamp.br%') OR
           LOWER(object_middlenames) LIKE LOWER('%dgrhcom@unicamp.br%') OR
           LOWER(object_lastname) LIKE LOWER('%dgrhcom@unicamp.br%') OR
           LOWER(object_namesuffix) LIKE 
LOWER('%dgrhcom@unicamp.br%')))) [pid 18358 on line 208 of 
"/usr/share/pear/Horde/Db/Adapter/Pdo/Base.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [imp] SQL  (0,0010s)
         SELECT alarm_id, alarm_uid, alarm_start, alarm_end, alarm_methods,
           alarm_params, alarm_title, alarm_text, alarm_snooze, alarm_internal
           FROM horde_alarms WHERE alarm_dismissed = 0 AND 
((alarm_snooze IS NULL
           AND alarm_start <= '2015-06-11 12:23:41') OR alarm_snooze <=
           '2015-06-11 12:23:41') AND (alarm_end IS NULL OR alarm_end >=
           '2015-06-11 12:23:41') AND (alarm_uid IS NULL OR alarm_uid = '' OR
           alarm_uid = 'coutinho') ORDER BY alarm_start, alarm_end 
[pid 18358 on line 208 of 
"/usr/share/pear/Horde/Db/Adapter/Pdo/Base.php"]
2015-06-11T09:23:41-03:00 DEBUG: HORDE [imp] Max memory usage: 
19398656 bytes [pid 18358 on line 608 of 
"/usr/share/pear/Horde/Registry.php"]

Dear Horde Team,

I have noticed this error on Internet Explorer and Google Chrome. I 
don't receive it from Mozilla Firefox, at least when I was testing.

Users start to complain that sometimes the "Error when communicating 
with the server" appears from nothing, even with the service working 
fine.
If the message appears with a new message window open, the user is 
forced to re-authenticate.

When I was simulating, the error appeared when I clicked "send" after 
typing a new message. On the second click, the message was correctly 
sent.

When the error appears, the horde.log contains the following error message:
2015-06-10T16:02:39-03:00 EMERG: HORDE [imp] Invalid token! [pid 32659 
on line 540 of "/usr/share/pear/Horde/Session.php"]

I'm working with CentOS 6 on both webmail and Imap servers.
The webmail server contains the imapproxyd daemon for faster authentication.
The IMAP server runs dovecot 2.0.9-8.el6_6.4.x86_64

I was browsing through the forum and I haven't found a similar 
situation with this error message.

Thank you.