External Drives for Mac Experiencing Data Loss with Maverick OS -- UPDATED FOR NOVEMBER 6, 2013

I see there are some solutions above, read the whole thread first.

If nothing seems to work for you, since it’s 2015 and Yosemite has been out long enough, then contact support contact WD directly and demand that they help you, or at least clarify the situation about WD drives and Yosemite.