I would make sure that you are using the latest version of the DLG Diag software and then try the test again. This error can happen if the software can’t properly detect/communicate with the drive. Can you test the drive in another system or possibly through an external enclosure (note that some enclosure can also give this error or not read SMART data properly). I would also try doing an extended test and see if that passes.
DLG 1.25
http://support.wd.com/product/download.asp?groupid=703&sid=3&lang=en
