809 Error Connecting to L2TP VPN from Win 8.1

I've configured the VPN on my Synology NAS, forwarded the necessary ports, etc. I'm able to connect successfully from my Android phone, so I'm pretty confident the server side is right. On the Win 8.1 machine, I have defined the AssumeUDPEncapsulationContextOnSendRule = 2 in the registry, I've set the recommended IKE and IPSec services to automatic, I've turned off IPv6 in the VPN connection configuration. I've also confirmed l2tp passthru is configured on the client-side router.

Anyone seen anything else?

Any idea?

Please help.

Thanks!

I didn't find the right solution from the Internet.

References www.cnet.com/forums/discussions/809-error-connecting-to-l2tp-vpn-from-win-8-1/

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