Coat a nonstick skillet with cooking spray; add 1 tablespoon margarine. Place over medium-high heat until margarine melts. Add 1/2 cup broth and mushrooms; cook over high heat until liquid evaporates. Remove from heat; stir in crabmeat, salt, and pepper.
Combine flour and 1/4 cup milk. Combine remaining milk and broth in a saucepan; add flour mixture. Cook over medium heat, stirring constantly, until thick. Remove from heat; stir in sour cream and next 3 ingredients. Stir in crabmeat mixture and artichoke. Spoon into a shallow 2-quart baking dish coated with cooking spray.
Combine breadcrumbs, Parmesan cheese, 2 teaspoons margarine, and paprika. Sprinkle over crabmeat mixture. Bake, uncovered, at 400° for 15 minutes or until lightly browned.