Example from ClientCertificateInstall CSP doesn't work?

Question

I'm using ClientCertificateInstall CSP in an attempt to install a new pfx certificate. I've read the document (as well as the older CSP), and I'm trying to make use of the example which the page gives at the bottom, beneath the description [sic] "Add a PFX certificate. The PFX certificate password is encrypted with a custom certificate fro "My" store."

And every time, I get a 400 for whichever '<Add>' appears last in my '<Atomic>' block. (I've tried re-ordering and omitting '<Add>'s, even supplying only a single '<Add>'.)

Naturally, I'm substituting my own data because the example doesn't provide the actual cert blob. You can see my entire XML in the attached 189797-my-commands.xml file. (If you want to confirm the validity of the pfx payload, it's a PKCS12 with the password 'testme'.) See also 189758-next-request.xml for the results of this command.

Do you have any idea what is wrong with my operation? Or is there another place I should be asking this question?