Has anyone experienced any issues installing a second CPU module?

The system boots with a single module ( I've tested booting using
either module in slot 0 )

When I boot with both installed I get an error from openboot:



Boot with diag-switch? set to true/max:


Diag Error:

POST toplevel failed:

CPU1
IO-Bridge0
Motherboard
Safari B



Hardware:

Openboot: 4.16.4
CPU Modules: USIII+ 900Mhz cu Version 2.2


Both CPU modules are good as I can boot using either in slot 0 - does
this mean that
the main board has a fault?

Thanks