WD Ultra Backup failed

I have a WD My Passport Ultra. I have changed computers therefore backup to the My Passport Ultra was not being added to. I therefore cleared the files in the drive of WD files. My WD Smartware is still recognising the drive but when I start backup it starts but after 11MB all the other files don’t back up and I get a result for each of them “The request due to a fatal device hardware error” even though the PC is fine. I wonder whether I have deleted a file off the My Passport Ultra that I should not have done?
Thanks in anticipation

I also get this plus it says it can only back up 50% as the ULTRA is under capacity. I am not able to edit and select specific files then to reduce the amount of data as the HELP indicates I can do. Select Files button does not open up for me, either. I cannot recommend a resolution.