VPN - "The L2TP connection attempt failed because security policy for the connection was not found"

DaveL-TOB 6 Reputation points

Connecting Windows 10 VPN to Draytek routers on numerous sites all returns the same error. I'm using PSK. Sometimes a reboot works, sometimes it doesn't. Have followed all steps in the similar message (The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer), but this error of mine is "security policy not found". Where is the security policy and why does it have a problem finding it sometimes??

Windows 10 Network
Windows 10 Network
Windows 10: A Microsoft operating system that runs on personal computers and tablets.Network: A group of devices that communicate either wirelessly or via a physical connection.
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