Right, I can see why the configuration might be an issue. By default, the FCT 4.3 client uses mode_config for the IPsec VPN connections. If you manually create a connection from the client, it may not work for your configuration on the FortiGate if it does not uses mode_config.
Since have a working 4.2 client configuration, here is what you can do to simplify the manual configuration on the 4.3.xx client:
a) use the VPN editor tool from 4.3.xx to export the 4.2 VPN configuration and then convert it to the 4.3 format
b) import the .conf file to the 4.3.xx client
Let me know how it goes,
L.C
Ling Lu