Hi Andy, can you please post the .3dm model file for your object instead of only screenshots?

For sweep you need to separate pieces out so that you are doing them with 2 rails a time.

For blend you need to hide any curves so that you can select edges and also the edge should belong to only one face so you should delete faces to make an opening before doing the blend.

I can demonstrate either of these on your file if you will attach it. If you need to keep it private you can e-mail it to me at moi@moi3d.com

- Michael