time machine does not work with kerberos

I want to backup some OSX 10.5 clients on a OSX 10.5 server with time machine. The backup volume is a share on OSX 10.5 server which is enabled as time machine backup destination.
Some OSX clients are in the same subnet and some clients are in a different subnet.
The backup-share has got these permissions: owner is the local administrator with read and write permissions, group is a time machine backup group with read and write permissions and others have no permissions.
The permissions are set in the admin-server tool.

Directory setup is ‚magic triangle, that is, ODMaster draws user info from active directory. The TM backup group,called tm_backup, is an OD-Group set on ODMaster.
I have try it with the SMB and AFP protocol.
The backup with time machine does not work. On clients in a different subnet you can not see any destination volume.
On clients in the same subnet you can see the destination volume in time machine, but the authentication do not work correctly.

Error Message:
Connection failed
There was an error connecting to the server. Check the server name or IP address and try again.
If you are unable to resolve the problem contact your system administrator.

But connecting the share via finder (command + K) works fine with kerberos authentication.
I am not sure how time machine clients connect to the server, but it seems that time machine not use the same way like Finders “Connect to Server”.

Is it possible to use the time machine backup with kerberos as authentification method?
Does anyone have a setup with kerberos or magic triangle (od-ad) run successfully?

Regards Mainchuh