If Proxmox won't start a VM with an error like this:
trying to acquire lock...
TASK ERROR: can't lock file '/var/lock/qemu-server/lock-102.conf' - got timeout
rm /var/lock/qemu-server/lock-102.conf
Then try to restart the VM and it should be good.
What we did above was find the lock file that is named lock-VMID (in our case 102) and deleted it to release the lock.........