I have an old 80gb Samsung external 2.5" hard drive, whice I've been using it on Windows machines for 2 years until switching to Mac a year ago. When I got the Mac, I formatted the drive to work on both Mac and Windows systems, and it has been running fine ever since. However recently, I've found that I cannot drag and drop or copy and paste files as I wish, whether within the drive or to other drives. Everything else seems normal. Any idea how to solve this problem? I've looked within Disk Utility to no avail. Thanks!