Unfortunately we don't own a recent version of Dreamweaver, nor are we experts on this product.  Hopefully other forum users will be able to provide a solution for you, but the right place for you to post your question would be the Dreamweaver support forums.  In the worst case you will need to rename your fwx files to asp while editing them, but  it would be nice if you could associate the fwx extension with Dreamweaver and direct it to use the ASP editor to display/edit them.