First guess is bad sector(s), sadly, right where you need them to be good. One thing to try is to run one or the other of the Linux live distros to see if you can access and pull the data that way. I used to have about 50/50 luck with that at the old job. If you can't get everything, you might be able to at least pull some of the files.
On that thought, have you tried pulling individual files, or just the whole folder? Sometimes one or a few bad files will keep everything from transferring if you just do a folder drag. Try and copy a few random individual files within the folder and see if they will transfer.