I have an external hard drive which keeps unmounting itself. How do I stop this.

Yes I have checked everything with WD. They even sent me a new replacement, but the symptoms are exactly the same..

I did install their Smartware (not so Smart in my view) but I have now removed it completely and just trying to run Time Machine.

I am running OS 10.7.4 on an iMac 27" 3.06 GHz. I have tried several USB ports in the back of the iMac incase one was faulty. Same results

I have turned the energy savers off.

Connected with the USB cable that comes with the WD drive . It is a USB 3.0 compatible with USB 2.0 cable.

I cannot seem to find any way to mount the "My Passport" volume when it has apparently tuned itself off.

I just Mounted it by unplugging and re plugging it in and it only stayed mounted for 1 minute.

When I am using files from the WD Drive and it is trying to dismount the volume an error message comes up and says:

"WD My Passport 0740 Media is in use and cannot be powered off.

Try quitting applications and try again."

However I have not done anything to try to quit, other than use some files.

No firewire available on the WD drive, only the USB 3.0

I am just trying to do the same Time Machine backup on my laptop to see if it works there OK.

It seems to be working OK on the Laptop but still having serious torouble on the iMac. The System Preference settings are largely the same.

The disc drive worked perfectly with the MAcbook pro (which is much older than the desktop).

{Thinks...} There must be a setting somewhere which turns off the hard drives, but I have then checked correctly in the systems preferences I think.