Supermicro.CPU is incompatable with host CPU.

[kalpana]

We've been running the servers for quite some time. Today a few servers were closed (switched off) for no obvious reason.
The error message showed: "the CPU is incompatible with host CPU: Host CPU does not provide required features".
On a working server, the settings: Configuration. "Model: qemu64".

From within the broken server, "Model: qemu32" is the only option.
Is it possible that a server forgets the types of CPU it is hosting...!? Sound strange for me! What am I missing??