/houdinihairprocedural1
)For instancing, the current procedurals process requires that the procedurals prim and their targets be active and directly editable on the stage. This means that instancing the same procedural setup multiple times can require some setup. There is an example available on the Hair Procedural's help card; I've also modified your hip file to demonstrate how to set this up, and added a few sticky notes.
That error about a missing attribute is actually because the procedural tries to import the instanceable geometry, which gives it nothing. So instead of saying "I have no geometry" it says "This attribute is missing" - while this is technically true, it's also very unhelpful. We are working on improving the error reporting messages for the procedurals and some of the underlying technology they leverage.
Hope this all makes some sense, and helps get you unblocked.