If a USB drive is not correctly safely removed from Windows it may not mount /operate correctly in the Mede8er. Many times you will not be able to 'Safely Eject' a USB Drive as some Windows program has a Locking Handle that is still accessing the drive.
We suggest you install a programmer called 'Unlocker'
http://www.emptyloop.com/unlocker/Once Unlocker is installed Navigate to the Drive (that will not Safely Eject) in Windows Explorer and right click and you will see the 'Unlocker' listing - select this it will show you what programs are locking the drive and you can select option to unlock it.
Once its unlocked then you can do a normal Windows 'Safely Remove' as normal.
Note Win8 Users Safe Removal in Win8 incompatible with the linux NTFS code. Instead use Utility to Eject the Mede8er (or shared external USB drive) - USB Disk Ejector
http://quickandeasysoftware.net/software/usb-disk-ejector