"Can anyone hazard whats going on here?"
I would hazard a guess that the drive is faulty. Chkdsk is not a very good test - it would be worth looking on the drive manufacturers site for a proper drive test programme. For instance Seagate have Seatools.
It would also be worth changing the data cable to that drive.
It might happen in one partition only if that part of a disk surface is damaged (clearly slightly).