[Evolution] TLS Client certificate authentification for accessing Addressbook/Calendar via WebDAV

[gdna]

Hello everybody,

        I am running evolution 3.10.4 on Ubuntu 14.04 LTS. I want to
        access a WebDAV Addressbook (and Calendar) via TLS Client
        Certificate Authentification, but I keep getting:
        
        This address book cannot be opened.  This either means that an
        incorrect URI was entered, or the server is unreachable.
        
        Detailed error message: Unable to connect to 'XXXXX': Error
        performing TLS handshake: Decryption has failed.
        
        
        I have added the Client certificate under EDIT --> Preferences
        --> Certificates --> Your Certificates, and the respective CA
        authority under EDIT --> Preferences --> Certificates -->
        Authorities.
        
        The same Certificate/server combination works on my Android
        phone with CardDAV Sync and CalDAV sync.
        
        When I am in the LAN, access to the same Addressbook and
        Calendar without SSL works on Evolution.
        
        The server runs egroupware 14.03.005. I am not the administrator
        of the server.
        
        Any suggestions on how to solve this are appreciated.
        
        
        
        Thank you,
        
        Denny