I am also experiencing this problem.
I have two WD MyBook World Edition 2TB drives, white with white LED. To each, I have connected a 1TB USB drive which is a WD My Passport Essential SE. I received all 4 drives three weeks ago, so the MyBook firmware is 1.01.18.
I am using both MyBook drives with all of my configuration work through the web interface that comes standard with the drives (Network Storage Manager). My configurations are to turn off everything (as much as I can) except the CIFS. With the CIFS service, I have created a folder share that goes to the 2TB hard disk inside the MyBook, and I am also using the default share name that appears when I plug in the USB drives: usb1-1share1. I have no quotes, no permissions, everything is open and public to the local network for these folder shares.
I am performing copies in the early AM via Robocopy. I have also done a lot of hand copying to test using Windows Explorer. I am running Windows Server 2008. I can always navigate in Windows explorer to see the MyBook drives and see the attached USB share. My copy jobs range from 30GB to 160GB. Everything works well when copying to the folder share inside the MyBook.
When copying to usb1-1share1, however, either by hand or via Robocopy, the network share name (usb1-1share1) eventually is reported to be unavailable. Thus, a 100GB Robocopy job might copy 50GB or even 70GB, but then error out on the rest of the files. But, in the case of an overnight Robocopy job, when I go to look at the situation a few hours later, in Windows Explorer I can navigate to the USB share. During the time when the network share name was unavailable, the CIFS logs in the Network Storage Manager show that the USB service was connecting and closing.
I should add that the MyBook drives are connected directly to 1GB ports on a Dell GB switch, which then connects to the server running Windows Server 2008. Some of the commentary in this tread discussed adjustments to the NIC on the computer, but that doesn’t apply here because the copy jobs start and work for a while.
To me, this has to be a problem with the firmware in the MyBook that manages the connectivity to the USB drive. I have a few other things to try in the mode of alternative component debugging, but I hope WD is watching this thread for attention in a future firmware upgrade.