I tried to start the VM’s after Update to Version 4.x it only stops with the Error
Failed to start VNC server: Our own certificate /etc/pve/local/pve-ssl.pem failed validation against /etc/pve/pve-root-ca.pem: The certificate hasn’t got a known issuer
The Problem ist easy and the Solution i had from here: https://forum.proxmox.com/threads/certificate-startup-problems.25815/
In my Case i use a Ceritificate from CAcert.org and this is not embedded as Trusted in the most Browser and System wide CA Positivlists. The Solution to fix ist to added the Certificat from the CA in PEM format at the end oft the File: /etc/pve/pve-root-ca.pem
But attention ! You have to write it with the Certificat Begin an Certificat End. The Original Certificat has to be there and only add the new one under the old one.
Now the VM starts without problems.