You're trying lie to the VM and tell it that it's running on a system with 24 physical sockets, each with a single core.
For reference, 2 sockets is the biggest AMD server that you can buy (these days), and Intel top out at 8. If you want a larger system, you could buy a SuperDome which can manage up to 32 sockets (before hitting other limits of UPI switching).
The various historical enumeration schemes can't encode that high, which is why there's a sanity check in XenCenter.
You typically want 1 socket, so select 24 cores / socket.