Windows 2012 R2 on IBM System x3650 M3 (type 7945)
You can migrate VMs started on certain hosts to all hosts in cluster but not back if the VM has been restarted on certain subset of hosts.
Live migration of "Virtual Machine VMNAME" failed.
Virtual machine migration operation for "VMNAME" failed at migration destination "HYPERVHOST". (Virtual machine ID XXX-XXX-XXXX)
The virtual machine "VMNAME" is using processor-specific features not supported on physical computer "HYPERVHOST". To allow for migration of this virtual machine to physical computers with different processors, modify the virtual machine settings to limit the processor features used by the virtual machine. (Virtual machine ID XXX-XXX-XXXX)
AES capabilities are not available on some of the hosts. VMs started on hosts without AES enabled can be migrated around without any issues but VMs started on AES enabled hosts can be migrated only between other AES enabled hosts.
Old versions of BIOS on these type of machines had AES disabled by default. There is no BIOS configuration switch to enable/disable it. To fix this BIOS needs to be flashed to version 1.10 or newer and then restored to default settings to enable AES.
VMware VMotion fails with "CPU is incompatible" error - IBM Servers