Looks like this code inside eas_sync_handler_new is failing:

    if (! eas_gdbus_client_init(&object->priv->eas_client, account_uid,
&error)) {
        g_object_unref (object);
        return NULL;
    }

Incidentally, that code fails to print the error and leaks it, which probably
explains why there is no real error message.

Do you run syncevolution inside a D-Bus session with DBUS_SESSION_BUS_ADDRESS
set?

syncevolution contacts activesyncd via D-Bus, and not being able to connect to
D-Bus is the only way how eas_gdbus_client_init() can fail.

Indeed, I can reproduce the error when DBUS_SESSION_BUS_ADDRESS is not set and
auto-launching D-Bus is impossible.

https://syncevolution.org/wiki/ms-exchange-and-kde-synchronization does not
call out that requirement explicitly. It's implied in that HOWTO because it
assumes that Akonadi and KDE are already working, which implies D-Bus.

For starting D-Bus, see for example this mail thread:
http://permalink.gmane.org/gmane.comp.mobile.syncevolution/4568