Error 781- The encryption attempt failed because no valid certificate was found

Symptoms:

1. When you attempt to manually establish a Layer 2 Tunneling Protocol (L2TP)/IP Security Protocol (IPSec) connection with a Windows server by using the Routing and Remote Access snap-in, you may receive the following error message:

Routing and Remote Access
An error occurred during connection of the interface.
The L2TP connection attempt failed because security negotiation timed out.

Also in the initiator computer, you may have the following Event:

Source: RemoteAccess
Event ID: 20111
Description: A Demand Dial connection to the remote interface <interface name> on port VPNx-y was successfully initiated but failed to complete successfully because of the following error: The L2TP connection attempt failed because security negotiation timed out.

2. When you attempt to establish an L2TP/IPSec connection by using Network and Dial-up Connections, the VPN client may display the following error message:

Error Connecting to <Connectoid Name>
Connecting to <IP address>...
Error 792: The L2TP connection attempt failed because security negotiation timed out.

-or-

Error Connecting to <Connectoid Name>
Connecting to <IP address>...
Error 781: Encryption failed because no valid certificate was found.

Resolution: 1. Make sure you have good connection between the VPN server and client.

2. Make sure the IPSec Policy Agent service is running. Or try to stop and then start it.

3. Make sure the certificate on the VPN server is a valid machine certificate. If the VPN server got a certificate during the Certificate Authority installation, this certificate is not valid for IPSec machine authentication.

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