>>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?
>
>When I Googled for this problem I found one message that says "Remove the VPN config out of the concentrator, then put it back." What do they mean by "concentrator"?

https://www.cisco.com/c/en/us/support/docs/security/vpn-3000-series-concentrators/4634-vpn-3000-faq.html

..I would make sure the ports are not being blocked by a firewall.