Thanks for the suggestions. It fails on any USB I plug into on both of my machines. But when I put my 500GB Seagate on the same cables it writes just fine.
I have tried disabling caching on ALL hard drives and just the external. None of these tweaks has helped. I am really starting to think it has something to do with the hard drive capacity; 1TB versus 500GB but I don't have anything yet to substantiate this hypothesis.