0xc0000225 error when trying to boot into the Windows Server 2008 R2 installer? And you're running on a Broadcom HT1000 based motherboard? Solution: hide/disable the XIOAPIC functions of the HT1000.

On the Supermicro H8SSL-i board this means going into the BIOS, Advanced tab, Advanced Chipset Control menu, "HT1000 Southbridge Configuration" menu, and finally changing the "Hide XIOAPIC PCI Functions" option to "Yes". Save the changes and reboot. (Note that this applies to v1.2 of the BIOS...which based on its age is probably going to be the last one ever released for that board...)

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