Read errors from external drive

[fiskah]

I have an external drive (500gb WD Passport) with some data on that I would like to access.

Unfortunately, whenever I try to copy a folder, I am just told that a "read/write error occured".

I tried repairing the disk with Disk Utility, but it just says that the disk is OK:

Verify and Repair volume “XXXXX”
Checking Journaled HFS Plus volume.
Detected a case-sensitive volume.
Checking extents overflow file.
Checking catalog file.
Checking multi-linked files.
Checking catalog hierarchy.
Checking extended attributes file.
Checking volume bitmap.
Checking volume information.
The volume XXX appears to be OK.
Volume repair complete.
Updating boot support partitions for the volume as required.

I have been able to extract a few files, but things are really slow, and some files fail to transfer.

Anyone got a clue how I can get the files off of my drive?