Error Message 0x80070003 on My Passport Backup Attempts

I am using Windows 7 and want to do a full system backup.  I have recently tried to uninstall the program, Dropbox.  The error is related to remaining Dropbox files.  I have used Windows Disk Cleanup, but still cannot get the backup to copy the system backup files to My Passport external hard drive.  I have used Windows system search to find the indicated file or files, but get no useful results.

Happy to report the following:  I found an empty file folder in the Libraries section of the Windows contents.  It had the title that was indicated with the error message 0x80070003.  I removed the folder; restarted the Compaq desktop computer; attached the WD My Passport to the USB port and started the backup.  The backup was completed successfully!