This appears to be a rather common problem, judging from searching the net, but I thought I'd ask about it here. I have two WD My Book external drives which I use for TM and CCC, one about a year old, the other a month. Starting several days ago, one of the two (the older one, which I have never had a problem with) is the subject of an entire column of "Disk Not Properly Ejected" error messages whenever the iMac wakes from sleep. The other drive exhibits such such behavior. Both icons continue to appear on the desktop, BTW. I've tried resetting SME and NVRAM/PRAM, changing USB ports, disabling Spotlight on the drive, etc. Nothing works except disabling putting the drives to sleep in System Preferences, which is of course not a solution. I've contacted WD and am waiting to hear back from them, after which I guess the next step is to contact Apple. I'm running Yosemite 10.10.1, BTW. Thanks for reading.