What does "The Finder can’t complete the operation because some data in “.DS_Store” can’t be read or written. (Error code -36)" mean?

It means that the drive has malfunctioned. Back up as much of the data on it as you can. You can try repairing the volume in Disk Utility, but the drive is suspect, even if the repair succeeds. If you ever have problems with it again, replace it.

I've had this a few times. Instead of trying to copy everything at once, see if you can grab individual folders. If that doesn't work then go into each folder and grab it's contents. If that also faisl then a drive issue is indeed likely.