Try plugging it in to another computer, move the files off of it and reformat it. Then move the files back on and try it on the tablet.
WD drives can be 'picky' sometimes. I have four of them myself. They are pretty good but when you switch them from machine to machine, they tend to stall out because the file allocation table gets messed up. Shouldn't be anything wrong with the drive.
If it still does not work, while it is plugged into the tablet, open the file manager (you will probably have it open already) and right-click on that drive on the list and tell it to "unmount" and unplug it. Wait a moment or two and plug it back in.