AutoCAD Inventor :: ILogic Multi-Value List From Materials

I am trying to populate a multi-value user parameter with a list composed of the various materials available from the iProperties "Physical" tab. So far I have this:

For Each material In iProperties.Materials        
Bracket_Material.Items.Add(material)        
Next
iProperties.Material=Bracket_Material
Running the Rule gets this error message:
Rule Compile Errors in Material_Rule, in _Mounting_bracket.ipt

Error on Line 2 : 'Bracket_Material' is not declared. It may be inaccessible due to its protection level.

I think I am doing the "Bracket_Material.Items.Add(material) " line wrong, but I don't know enough VB to fix it. It seems to me it IS declared in the Parameters table - isn't adding the parameter to the parameter table sufficient to declare it?

Eventually I want to add the Bracket_Material Parameter to a form so the user can select material from drop down list and assign it to part.