What is it that is selected? Space after applies to all the paragraphs within the selected range.
If you want something that applies only to the last paragraph in the range then you must tell the macro to limit to that paragraph e.g.
Code:
Selection.Paragraphs.Last.SpaceAfter =
or provide the index number of the paragraph e.g.
Code:
Selection.Paragraphs(3).SpaceAfter =