solved .. CPU type is wrong
although the Wiki https://pve.proxmox.com/wiki/Qemu/KVM_Virtual_Machines reports that
x86-64-v2-AES: Compatible with Intel CPU >= Westmere
my CPUs are 2 x Xeon X5650, the VM will not start
So, something is wrong, the wiki, or something in Proxmox is not working correctly