I was trying to put VMware ESXI 5.1 on the dedi I got yesterday. This error kept popping up during the ESXI installation. The dedi is using Dell 5/i raid card with four 1T hard drives in 4 disks Raid-5. After a few times installation failures, I found out the VT-d setting in the BIOS was causing the problem. Turn it off, install ESXI, all good. You can turn it on later after finish the installation.