[kronolith] Import of .ics file not working

[Goodkat]

 I installed the horde groupware package.
I did not install the PECL
files recommended in the installation instructions.
Besides that, i
installed all as recommended.

When trying to import an .ics file to
kronolith,
i get the following message from the debian terminal:

HORDE:
[kronolith] Class 'Horde_HashTable_Vfs' not found [pid 23748 on line 34
of "/usr/share/php/Horde/Core/HashTable/Vfs.php"]

My system is a LAMP
Server with
Debian wheezy
Apache 2.2.22
Mysql 5.5
PHP 5.4.4

What do i
need to configure or install?

Thanks, goodkat