After a number of memory upgrades on our G6 servers I experienced an issue during the boot process whereby a number of DIMM slots were being reported as having 207 memory initialization errors.
I re-seated all the memory modules thinking that perhaps a module was not pushed in enough and after further research ensured that the BIOS was up to date.
Finally, I used different memory replacing the 3 new modules with a different set of 3 modules. This worked.
By process of elimination it turned out to be a faulty new module that was failing a bank of 3 modules. Even new HP memory can be faulty and is worth checking!