WD Passport Essential & Time Machine - disk unmounts in the middle of back-up

WD External Drives External Drives for Mac
1

When I first bought the Passport Essential (Dec 2011), I installed the Mac software and used it to back up with Time Machine no problem. I have not been able to again since. Each time I attempt to back up it begins and within a couple minutes stops and TIme Machine says it will next back up when it finds the disk. Yet, the disk is still attached. 

As per the advice of several forums, I reformatted the disk with disk utility, made sure there was only one partition and tried again. No luck. I have formatted with the SmartWare software. No luck. 

Anyone have any advice? Does this drive not work with Mac? The first time it was used, when it worked, I was using Snow Leopard, but I attempted to do a follow up back up with Snow Leopard, Lion and now Mountain Lion. None of these have worked.

Help!!! So frusterating. 

2

Have you tried using the drive in a different computer? And also using an additional USB cable? Do you have the same issues if you transfer the files manually instead of using Time Machine?

3

nother box keeps trying to tell me I can’t open the VCD and have to download up to date firmware- I thought the beauty of it was that it downloaded updates on its own. It seems you can manually type in password each time you want to do a backup which again defeats the object of a set and forget