I have a question on a fairly sophisticated family that I've simplified to what you see in the attached RFA (this is a Revit 2008 question).

 

The issue is that I have two extrusions (extrusion, hollow extrusion) which are nested into my parent family (Problem Family). Revit has the capability to have families themselves as parameters - so if I want, I should be able to swap out hollow extrusion for extrusion and vice versa. So - I've created a parameter called Extrusion and Type and then four types. I've brought in my extrusion and then placed, aligned and locked it to the height ref. plane so that it will move accordingly as the user selects the various types. 1'H Extrusion should move the extrusion family to 1' off the ground. 1' H Hollow Extrusion should have my hollow extrusion family 1' off the ground. But that's my problem - when I change my parameter (Extrusion Type) to Hollow Extrusion - it breaks. However there is no problem in adjusting the height - if I move to 5' H Extrusion, everything works fine - it's just switching from one rfa to another that seems to be creating a major issue.I've seen the Revit Help document on this: Creating and Applying a Family Type ParameterNo dice. Anyone have a clue how I can get this to work and what I'm doing wrong?