I didn't say you'd reformatted it - I asked how you formatted it in the first place!
Not that it matters - you've answered the question indirectly. For partitions > 256GB you have to use XBPartitioner 1.1 to format the disk, and it sounds as though you didn't. The consequence is that you get disk corruption when the disk has more than 256GB on it, and it sounds as though you've reached that limit.
Don't try to write anything else to the disk. If there's anything on there you don't have backed up try to recover it. Photorec might be able to recover any deleted files. Once you've done that, reformat the disk with XBPartitioner 1.1 (it has to be 1.1, not the earlier version), and start again. This post has been edited by Heimdall: Mar 1 2009, 02:54 AM