Ah, now we're getting somewhere! I get the same error on my iPad 2, so it isn't an iPad 3 issue, per se. Looking more closely after downloading the stencil on my Mac, it turns out that it is a zipped up folder containing several stencils, and the iPad app apparently doesn't know how to deal with that. You can download the file to your Mac or PC, unzip, and email the various stencils to yourself (or use iTunes to move them).
I tried out a handful of the stencils after I did this, and they appear to load correctly.
I agree that it is confusing that the GraffleTopia page lists them as working with the iPad app, but you can't download them directly as is usually the case!