Incorrect function.(0x80070001) while performing a Vista Backup to a USB external harddrive

When running a scheduled Vista Backup to an external harddrive, I get the the following error message.

The backup did not complete successfully.

An erroroccurred.  The following information might help you resolve the error:
Incorrect function. (0x80070001)

Any suggestions or ideas?

I have previously run successful backups to this drive before, and I'm currently running a disk check on the drive.

The system is a laptop with Widows Vista SP1.

These error messages are usually generated if an EISA partition on your hard disk is marked as active.

1. Open Start menu and then in the Start Search box, type diskmgmt.msc.

2. Next, in the Programs list select diskmgmt.msc to display the Disk Management window.

   Note: If prompted, type in the administrator password or click Continue.

3. In the Disk Management window, right-click on the primary disk partition that you want to make active.
4. From the right-click menu, select Mark Partition as Active.
5. Close the Disk Management window and then reboot your Windows Vista computer by using the Windows Vista DVD.

6. When prompted, specify your preferred language and then click the Next button.

   Note: The repair process should start automatically in most cases. At times, you may have to make your choice of action if the System Recovery Options menu is displayed.

7. If the System Recovery Options menu is displayed, select Repair your computer.
8. Next, select the operating system you want to repair in the System Recovery Options dialog box, and then click the Next button.

9. After the repair process completes, click the Finish button.

10. Next, restart your Windows Vista computer from the hard disk.

11. After the computer restarts, log on to it and then attempt to perform your backup activity once again.

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