Canbt move folder onto my book from desktop

I can open and view the contents and folders of MY BOOK no problem.  However, when I try to add a new file or folder by dragging and dropping it won’t go.  The drive does not appear to be locked.  When i go to the WD smartware folder and hit drive unlock, it says the drive is not locked.  the lock on the front of the drive is not lit.

It has been a while since i added anything to this external drive.  now I can’t add anything to it.  Help?

Was this drive originally used on Windows? if so it will be read only on Mac. If that was the case download NTFS-3G