[horde] Problem with Kronolith

[info@web-front.de]

Hello,

after the login to Horde and a klick on the Menulink "Kalendar" i see this Error-Message on the Desktop:

*Warning*: in_array(): Wrong datatype for second argument in 
*/var/www/horde/kronolith/lib/base.php* on line *134*

After a second klick is the error-message vanished.

How can I fix It?

Kind Regards
Thomas