C++ webservice client always return SOAPCLIENT_PARSE_ERROR, please help!!

I have a very simple webservice that returns an even more simple xml
object. I use sproxy.exe to build a reference to the sole method in the
service but continute to get SOAPCLIENT_PARSE_ERROR during the call.
Anyone have any ideas what would cause this?

The webservice is c# the client is C++ using atlsoap

The trace returns this:
ATLSOAP: CSoapRootHandler::GetElementEntry -- element not found:
sipuri.

the returned structure is, this is obviously serrialized to very simple
xml

    public class Contact
    {
        [XmlElement()]
        public string name;

        [XmlElement(IsNullable=true)]
        public string sipuri;

        [XmlElement()]
        public string phone;

        [XmlElement()]
        public string mobile;

        [XmlElement()]
        public string email;
    }

    public class ContactGroup
    {
        [XmlElement()]
        public string name;

        [XmlElement("member", typeof(BCMBuddy))]
        public BCMBuddy[] buddies;
    }

    [XmlRoot("contactlist", Namespace="http://listns.oururl.org")]
    public class ContactList
    {
        [XmlElement("dummy")]
        public string dummy;

        [XmlElement("group", typeof(ContactGroup))]
        public BCMBuddyGroup[] groups;
    }

thanks,
Rob