Mix coconut and pecans. Put in bottom of greased 13x9 inch pan. Prepare cake mix as directed, pour over coconuts and pecans. Cream together margarine and cream cheese, add powdered sugar. Spoon over top of cake mix. Bake 35 to 40 minutes at 350 degrees. Let cool 10 minutes. Place serving platter over pan, invert so cake is upside down on platter. Do not cut until cake is cold.