I had the same problem, but the WD support line resolve it. Maybe it will work for you.
If you have any data on the WD drive be sure to copy it off before following these steps to re-format your drive for compatibility with Mavericks.
With Mavericks OS based Macintosh off, plug in My Passport for Mac and boot-up the computer.
Open Disk Utility (located in the Applications > Utilities folder).
Select the My Passport harddrive on the left side of the Disk Utility window.
Select the Partition tab at the the top of the Disk Utility window.
Under Partition Layout select 1 Partition.
For Name enter “My Passport” (or whatever you want to call your drive).
Click on the Options button and select the first option “GUID Partition Table” and click OK.
Click on the Apply button in the lower right of the Disk Utility window and wait for drive to be reformatted.
That’s it.
