"Remove Vault" greyed out ...

I have successfully re-established my Aperture Library on a new Lacie 500GB extHD. I've also successfully established a back up Vault on a new Lacie 300GB extHD. I'm trying to remove the original backup vault from the old Lacie 150GB extHD (all ext HDs daisy chained-thru 400/800 cables as appropriate). But the File/Vaulty/"Remove Vault" is greyed out. I've tried restarting the computer, shutting down and starting up Aperture with no success.
Any suggestions?

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Orignal From: "Remove Vault" greyed out ...