However, when trying to back up your files, you may get an error saying Windows Backup failed while determining libraries location of one of the users included in backup. Details: The device is not ready. You can see an error code 0x81000031 on the screen.
This error occurs because you have added custom libraries that aren't accessible when you perform a backup. Custom libraries may be not available if these libraries are on removable media or an unavailable network drive. As a result, the computer cannot access them during the backup process.
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