So you've been visited by the much dreaded CRC — Cyclical Redundancy Check error, most likely encountered while copying files between hard disks. On Mac OSX, this will usually appear as some cryptic permissions message with an Error –36.
To cut the geek-speak, this simply means that you hard disk may have certain files that may have "bad sectors", or are corrupted in other words.
Fortunately, this is a common enough problem in our technically advanced world of external storage. I recommend solving this on Windows (I use both XP and OSX Leopard at the time of this writing).
Step 1: CHKDSK
Use what Windows offers you by default. The chkdsk command. Just open an MS-DOS command prompt window and go to the drive you wish to check (I'm hoping you already know your way around a command prompt; if you don't please consider Step 2 below). With the command prompt showing the drive letter of the disk you wish to check, enter this command:
e:> chkdsk /R
Here, "e:" is my drive to be checked. The "/R" attribute asks the chkdsk command to "recover" whatever bad sectors it finds during its scan. In most cases, and if you're lucky, this ought to do it.
Step 2: CDCheck (Free)
Only if the problem you were facing still remains after you have run the chkdsk command, should you consider doing this. This is a freeware program that makes it super-easy to check/recover your disk. It can be any disk–your current hard disk, a CD or a DVD, or even an external hard disk. The interface is pretty simple as you can see in the screenshots here.
Step 3: SpinRite (US$ 90)
If all else has failed, just save yourself some heartburn and go straight to SpinRite. This is hands-down the best software for this purpose, as anyone in a dire need of data recovery will confirm. I would trust any piece of software from GRC. Only catch: it's not free, but when you use it you know why it's worth every last cent. It gives you a simple option to save an ISO file, which you can then easily burn on to a CD using any CD writer tool (including Windows' own right-click). Then reboot your machine so it starts from the CD. SpinRite will automatically report and recover whatever is recoverable.
Next Steps
Basically, a CRC error is the beginning of the end. If this is on an external hard disk, I highly recommend that you consider backing up the data immediately.