Hello Billwill - first, I'm assuming that you mean a USB 'flash drive' and not an external HD - correct? Second, as already suggested check the current formatting, likely MS-DOS (FAT32) - use Disk Utility to see what the current format is on the drive (see my attached screen capture on the app opened w/ a 32 GB Kingston flash drive attached to my MBPro - blue arrow shows the current formatting; red arrow another option, i.e. the OS X specific 'Mac OS Extended...).
If you plan to use this only on Apple OS X devices, then you could format w/ the Mac option or just leave on FAT32 if using Windows computers also - the only issue w/ the latter is that there is a 4 GB file size limitation - SO, let us know what you plan to use the drive for and what is the file size maximum needed? Dave
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