Activesync not working

Hi,

as already written in my previous message, I've successfully installed 
Kolab3 on Debian Wheezy, mail sending/receiving and webmail works fine.
Now I've install the package kolab-syncroton to use ActiveSync. At 
first sight, everything looks fine. I'm able to log-in to 
/Microsoft-Server-ActiveSync and get the message "It works! Your userid 
is: 2 and your IP address is: x.x.x.x.".
My two devices (Android 4.0 and Nokia N9 with MeeGo) are able to 
contact the server, the account can be created and the devices are shown 
in the roundcube settings. But as soon as the device starts syncing (the 
Apache access log shows that the device syncs) an error occurs. Android 
just tells me "Server not available", MeeGo has some more information: 
"System error" and "Folder on server not available".

Is there anything I can do to debug this?

Cheers,
Tobias