Softimage Xsi: Problems with Biped Guide Rig

So everytime I go to create a rig from a biped guide, it craps out with "Error: Argument 0 is invalid". I thought I might be "messing up" the guide, but creating a rig from an untouched guide still gives the error (just tried with a new scene and it works fine without altering the guide, tried exporting my model, and importing it into a new scene with no luck). The only rig that works is the traditional one. Anybody have any ideas as to what's wrong? I'd really like to use the rig, it seems to do exactly what I need.


Thanks,

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