1In shallow glass or plastic dish, mix steak sauce and brown sugar; reserve 2 tablespoons sauce. Add beef to remaining sauce (about 1/4 cup); turn to coat. Cover and refrigerate, turning beef 2 or 3 times, at least 1 hour but no longer than 24 hours.
2Heat gas or charcoal grill.
3In 2-quart microwavable casserole, place potatoes and water; cover. Microwave on High 3 to 5 minutes or until potatoes are just tender. Place potatoes on sheet of heavy-duty foil. Spray potatoes with cooking spray; sprinkle with rosemary, thyme and paprika. Wrap securely in foil.
4When grill is heated, place beef and packet of potatoes on gas grill over medium heat or on charcoal grill over medium coals; cover grill. Cook 7 minutes. Turn beef and potatoes; brush reserved sauce over beef. Cover and grill about 6 to 8 minutes longer for medium beef doneness; remove from heat. Sprinkle salt and pepper over potatoes.