I got the same message. I thought the labels on the DVD's meant the OS you were using to load and ended up loading 32-bit. I went into BIOS and cancelled all boot selections except the DVD drive. Put the 64-bit DVD in and rebooted. It ended up booting just fine. I had the original OS on an IDE drive and started 7 on my RAID 0 array, so when I reloaded with 64-bit, it was only writing on top of the first attempt (32-bit 7), so original OS remained intact. It was XP Home that I had to buy to get my new computer build going until 7 was released (lightning trashed the old MB and RAM).