Are you trying to access the device by means of a File Transfer Protocol (FTP) connection? If so, the WAN address is not enough.
First, please ensure FTP access is actually enabled for the share you would like to access, then the syntax would be ftp://username:password@WAN.IP.Address (Example: ftp://admin:password@xxx.xxx.xxx.xxx).
Also, please bear in mind that the WD My Book World Edition will use port 21 for FTP by default.
