Might be your device is improperly removed from a computer, the OS sets a “marking bit” on the drive showing that it was not properly removed. If this drive is connected the WD TV it will not read the drive because it reads that marking bit that shows it was improperly removed. So, Connect the drive to a computer, and safely remove the drive. This will change the marking bit to show that it was properly removed. The WD TV should then read the drive.
However you can also check the compatible USB devices for the WD TV HD Media Player
It helps, thanks so much.