There are fairly regular posts from people who have similar problems. The advice generally is to try the alternate CD, which uses a different partitioning tool, and seems to have less problems. This worked for me. Anyway, you have yours solved now, so that is good.

Interesting that you say you are using a Samsung HD. I am too, also in my NAS, and am determined never to buy that brand again. They work, but I had issues with both machines having trouble finding the disks.