My Book Essential 1TB won't copy

I recently had to format My Book and I did struggle. I have noticed over the past two weeks that I cannot copy ‘large’ files from my desktop to the external, i.e. movies. I have even went to the extent of archiving the files into 15mb pieces and move them onto the drive at incriments of 5. And when I’m extracting on the external disk it gives me an error saying that such and such ‘part’ are corrupt, so I slowly copy them over again. This time individually, then I extract to proceed to the next ‘corrupt’ archived part. I finally reached ‘part 39’, even after repetitive copies it still doesn’t work for me. I can not move ‘large’ files onto the external. I read on the forum earlier and their response was, “check the under policies and make sure ‘better performance’ is check instead of 'quick removal.” In my case the ticked box was ‘quick removal.’ I am getting extremely frustrated with my issue. It has been a constant nuisance to me. I know there is something I’m not doing. Such as, I probably didn’t format the disk correctly, I don’t know. But any inputs regarding my problem I would have uberous gratitude towards. Thanks.

I don’t think I mentioned that when transfering large files it usually progresses to 33% - 66% then the transfer data rate drops to 0 and does abosolutely nothing but keep a progress dialog box open.