Does the IPsec configuration also require Pre Shared Key? Please share a screenshot of this.
Also, verify the connectivity from the RUT950 to the server. They should be able to connect with ping.
If this works fine, do some tests again trying to connect to L2TP after IPsec is up, and download the troubleshoot file (System > Administration > Troubleshoot > Troubleshoot File). Please, share this file on the first post so we can check the logs.