Melt 2 ounces of margarine in a large soup pot. Add chicken and saute until cooked half way. Add sausage and vegetables and cook until vegerables are tender. Add chicken broth and seasonings and bring to a simmer. Make a black roux in a seperate pan. Heat butter very hot and add flour. Turn heat down to medium. Stir frequently until roux beomes very dark, almost black in color but not burnt. (This takes practice) Slowly alternate soup into roux and roux into soup whipping until thickened and smooth. Simmer for 30 minutes. Add shrimp and okra. Simmer until shrimp is cooked about 2 minutes. Remove from heat. Dissolve Gumbo file powder in water. Slowly stir into soup. Serve plain or with white rice