>>>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?
>>
>>If it's happening with multiple VPN customers then the problem is at your end, not any VPN concentrator.
>>
>>Can you try again with your antivirus disabled, especially any network filtering/firewall function?
>
>Yes, this is the first thing I tried yesterday, to shut down Avast (my AV) but it didn't make a difference. And indeed it is my problem because I have another computer with the same version of Cisco VPN and yesterday the other computer worked. And bothe computers are on the same Wi-Fi. I may have to uninstall the Cisco VPN on my PC and install it again; just to see if it will make a difference.

Just for reference, Shrew Soft has a free Cisco-compatible VPN client at https://www.shrew.net/download/vpn . Note that for Windows 10 you need to make a registry change before installing this product. I've used it fairly extensively and it works well; it can take a bit of time to configure, though.