What's the PBA# of your board? Check Server Products — Important information on support of Intel� Xeon� Processor 5300. If it's lower than -801, there is no solution but to change the board or CPU, since it's a hardware limitation.
My PBA# is : D46952.702.
I realized a test on one of my server.
I made a downgrade of BIOS (via the following page: www.intel.com/support/motherboards/server/sb/CS-023585.htm) for the version S5000XAL.
Resul : no error message in BIOS, both processors are recognized. My server W2K8-R2 knows eight processors, as well as Sandra Sysoft.
Does it seem to you correct to think that the downgrade was benecial ?