If I try to create a new folder on my external drive it says that I don't have the sufficient access privileges. I only have one log in on my Mac and I've only used the drive on this Mac. However the drive was another one sent back from WD after mine broke and it's clearly refurbished - maybe somehow it's still "linked" to the last owner? I can copy to it etc though. If I do a ls -l /Volumes then I notice that the drive instead of having my name against it like all the other drives it has "root" instead and instead of saying "Staff" like all the other drives it says "Wheel".