How to fix Proxmox error “401 permission denied – invalid PVE ticket”

NOTE: This fix may not work for everyone but as it helped me finally solve a problem when messing around with clustering after looking for quite a while, this post is to make it easier for the next guy to find

In the following order run:

• systemctl stop corosync pve-cluster
• systemctl stop pvedaemon pveproxy pvestatd
• systemctl start pve-cluster
• rm /etc/pve/authkey.pub
• rm /etc/pve/authkey.old – don’t worry if it cant find a file to delete here
• systemctl start pvedaemon pveproxy pvestatd

You should now (hopefully) have access to your web interface again

The information here is copied from this post on the proxmox forums.