"Value cannot be null. Parameter name: pUnk"

I a bit confused.  Your screen shot looks like you've got an EXCEL sheet imbedded; I get the component wizard window if I'm inserting a new component.

If you have the this

in a sheet already try this:

• right-click on the component.  You should get a dialog with

                                 "add input variable"

                                 "add output variable"

                                 "properties"

   and a bunch of other options

This should let you define your inputs

But where is your Mathcad worksheet with this error?