Error 0x80070002 Using Windows Backup

I am using Vista Home Premium SP1. I have been using the backup program

found in "backup and restore center" to backup to an external drive called

"MyBook" successfully. For no reason that I can recognize, backup attempts

have started getting me the message "The system cannot find the file

specified ... (0x80070002). ... MyBook (G:). This happens whether I try a

partial or a full backup.

Is the file which has become corrupted on my computer, or is it out on

MyBook?

What do you advise me to do?

Thanks.

Spencer

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