How to Erase Drive - 'drive is currently in use...'

I am unable to erase My Passport Essential using WD Smart Ware revision 2.019. Under Settings>Drive Erase, I keep getting the error ‘The drive is currently in use. Close and applications or windows currently using the drive, and then try again’.

After erasing I want to continue to use the back-up function so I do not want to format the disk using windows.

Anyone any ideas? 


Make sure in task manager to close every application related to the drive. Also formatting the drive with Windows does not affect the drive backup system, you can reinstall and continue the process.