We have seen this error only when trying to run Disk First Aid on an MFS-formatted volume. You can verify that the volume is HFS by looking at the left side of the two lines below the volume information when your disk window is open. There will be a pixel on the left side indicating that the volume is an HFS volume. The absence of a pixel means you have an MFS volume or you are running System 7.
If the volume is HFS, use a more current version of Disk First Aid--version 1.4.3 or above.