I am using a Macbook Air.
When I open an existing file on the external drive, it brings up the file without any problems. When I save the file with a different name, however, the new filename is not seen, yet when I do a search for the newly written file, it is show to be written on hard drive. In other words, the file has been successfully saved to the drive, but it can not be seen.
I did a verify on the disk utility, and it said the drive was fine.