Intel S5000PSL support for E5420 CPU ?

Hi,

I have a Intel S5000PSL Server mainboard and like to upgrade he CPU's to Intel's E5420.

The mainboard description say that BIOS version 84 or later wil support the series 5200 and 5400 CPU's.

If I put them on the board it wont boot and I receive error codes like:

19A = Fatal Voltage mismatch

There is also the thing about non-refresh board wich is not entire clear for me.

Is this a hardware or software limitation problem?
Please let me now