Erro Code 100021

I operate a computer with the MicrosoftXP programme and am using Comodo Backup with a Seagate external USB. It has 300GB capacity with 127GB free. I schedule a nightly backup. The system has operated well for the year that I have had it. We now have a problem.

When I turn in the screen after the backup is normally finished (about 6 hours) there is a message that the backup failed with error code 100021. When I click “Finish” or click to close the program, I am told that any changes made will be deleted. So I close the program believing that the backup has failed.

I have checked the external drive and find that the last document I worked on the previous night has in fact been backed up successfully, despite the error message code 100021.

Please advise how to remedy this problem.


This error means a device is not ready.
Please attach a screenshot with the error.