permissions and groups

[Gustav Spellauge]

hello,

how is it possible for a user to grant permissens on one of his objects
(mails, addressbooks, .., tasks) to a group of users.

- created a group 'testers' containing 3 users using kolab-webadmin

one of our users tries to grant access to his addressbook:
- he clicks the +-sign, ticks the user-option and enters testers into
the imput field, testers is displayed prefixed by the group symbol in
the selection box
- he selects testers and the content of user input field chages to
group:testers,
- when he clicks the save-button an errorbox with the string 'Unable to
add access rights' is displayed. changing group:testers,to group:testers
(without the ,) does not help.

is there anthing i cold do to fix this.

tia, gustav