>I have been using Cisco VPN Client version 5.0.07.0440 for a long time, connecting to many customers.
>
>Since yesterday, I am not able to. When I click on Connect I get message
>
>

>Secure VPN Connection terminated by Peer
>Reason 427: Unknown error occurred at Peer
>

>The number 427 may change to another number if I try to connect to another customer.
>
>What would you suggest to try to resolve?

Is this on Win10? If yes, then the Cisco VPN client is not compatible on its own. Solutions exist with SonicWall
for example: https://itthatshouldjustwork.blogspot.com/2015/07/cisco-64-bit-vpn-client-on-windows-10.html