CalDav Sync Problem only on mac

Hi,
I'm running an oc server 9 and use several clients to sync calendars and contacts. Actually I've got the Problem, that only the caldav sync on mac doesnt work. Cards work fine and also calendards on windows or android work, on mac I get the message: No caldav calendards found on server.
I use the deeplink to the calendar and also tested the same calendar on a windows based system, and there it works properly.
So any idea why contacts work and calendars don't?
Thanks
chris

Probably needs some debugging on client-side. Are there any mac os x support communities out there which could help you with this task?

Not sure, but I'll have a look to it.