IBM xseries POST message swap CPUs

[MrTwig]

I have a working xseries 335 which had one 2.4 Ghz Xeon.
I took the second CPU from a duel 2.4 Ghz 335 and installed it in the working one.
It works. POST and Windows device manager shows two CPUs and a benchmark shows a very significant speed increase.
However, soon after power up POST shows the following messages.

CPUs not in recommended order.
Move CPU in slot 1 to slot 2
Move CPU in slot 2 to slot 1

My question is why should that be so?
Both CPUs are 2.4 Ghz Xeon.

Is it worth moving the CPUs?
I thought about swapping the CPU 1 in each machine so the two CPUs that were in the dual machine would be back together.

Any advice?

Thanks

 

[LarryTheCucumber]

Check the CPU Stepping in the BIOS, they are probably different.

 

[MrTwig]

You are probably right.
Thus I think I should swap the CPU 1 in the two machines.