I was helping a friend and wanted to copy some of his MAC files onto my USB thumb drive. No matter what I did, it would not work. Note that this is a larger 64 gb drive. I put in a smaller 4gb drive and the files were copied without any problem.
The problem is that the larger thumb drive is formatted in NTFS which a MAC can read, but cannot write to. To do a copy, you need to have a FAT32 drive which my smaller drive was setup as.
Here’s a nice video explaining the problem and solution.