Event accept fails in roundcube on kolab 2.4

[Dirk Werner]

Hi,
when accepting an event in the invitation mail in roundcube, I get an
internal server error, the following is logged in /var/log/httpd/error_log

[Thu Oct 25 17:53:40 2012] [notice] SELinux policy enabled; httpd
running as context system_u:system_r:httpd_t:s0
[Thu Oct 25 17:53:40 2012] [notice] suEXEC mechanism enabled (wrapper:
/usr/sbin/suexec)
[Thu Oct 25 17:53:41 2012] [notice] Digest: generating secret for digest
authentication ...
[Thu Oct 25 17:53:41 2012] [notice] Digest: done
[Thu Oct 25 17:53:41 2012] [notice] Apache/2.2.15 (Unix) DAV/2
mod_nss/2.2.15 NSS/3.13.1.0 Basic ECC PHP/5.3.10 mod_ssl/2.2.15
OpenSSL/1.0.0-fips configured -- resuming normal operations
[Thu Oct 25 17:55:19 2012] [error] [client 192.168.40.167] File does not
exist: /usr/share/roundcubemail/plugins/contextmenu/skins/larry,
referer: http://192.168.40.1/roundcubemail/?_task=mail
[Thu Oct 25 17:55:27 2012] [error] [client 192.168.40.167] (36)File name
too long: Cannot map GET
/roundcubemail/plugins/calendar/skins/larry/images/calendar.png HTTP/1.1
to file, referer:
http://192.168.40.1/roundcubemail/plugins/calendar/skins/larry/calendar.css?s=1347454225
[Thu Oct 25 17:55:27 2012] [error] [client 192.168.40.167] (36)File name
too long: Cannot map GET
/roundcubemail/plugins/calendar/skins/larry/images/loading_blue.gif
HTTP/1.1 to file, referer:
http://192.168.40.1/roundcubemail/plugins/calendar/skins/larry/calendar.css?s=1347454225
[Thu Oct 25 17:55:39 2012] [error] [client 192.168.40.167] PHP Fatal
error:  Call to undefined method rcube_imap::get_headers() in
/usr/share/roundcubemail/plugins/calendar/calendar.php on line 2178,
referer:
http://192.168.40.1/roundcubemail/?_task=mail&_action=preview&_uid=2&_mbox=INBOX&_framed=1
[Thu Oct 25 17:56:18 2012] [error] [client 192.168.40.167] (36)File name
too long: Cannot map GET
/roundcubemail/plugins/calendar/skins/larry/images/calendar.png HTTP/1.1
to file, referer:
http://192.168.40.1/roundcubemail/plugins/calendar/skins/larry/calendar.css?s=1347454225
[Thu Oct 25 17:56:18 2012] [error] [client 192.168.40.167] (36)File name
too long: Cannot map GET
/roundcubemail/plugins/calendar/skins/larry/images/loading_blue.gif
HTTP/1.1 to file, referer:
http://192.168.40.1/roundcubemail/plugins/calendar/skins/larry/calendar.css?s=1347454225
[Thu Oct 25 17:56:20 2012] [error] [client 192.168.40.167] PHP Fatal
error:  Call to undefined method rcube_imap::get_headers() in
/usr/share/roundcubemail/plugins/calendar/calendar.php on line 2178,
referer:
http://192.168.40.1/roundcubemail/?_task=mail&_action=preview&_uid=2&_mbox=INBOX&_framed=1

This is logged when pressing the accept button, any ideas?
Regards
Dirk