I ran across a bug recently when I created a VM with the latest versions of ESXi 5.1.0-838463, Client ver 5.1.0-860230, vCenter ver 5.1.0-880146. If you create a VM for a Windows 2012 Server OS for some reason Record/Replay is disabled and you cannot put it into Fault Tolerance mode. I found a workaround though. You delete the VM from inventory, then recreate the VM as a Windows 2008 R2 Server and use the VM that you deleted from inventory's origional disk instead of creating a new one. Then enable FT. Then go into settings and change the OS back to Windows 2012 Server. Problem Fixed. Hopefully they will fix this soon.
Jimmy S.