Preheat oven to 350. Grease a 9x13 inch baking dish. Combine enchilada sauce and sour cream in a medium saucepan. Cook over medium heat, stirring constantly, until cheese has melted and mixture is smooth. Remove from heat.
Spread approximately 1/2 cup enchilada sauce mixture on the bottom of prepared baking dish. Layer with 4 tortillas, 1 cup enchilada sauce mixture, 1 cup chicken and 2 cup cheese sauce. Repeat layers, then top with remaining tortillas, enchilada sauce mixture and chhese sauce. Cover with foil.
Bake for 40 minutes. Uncover;let cool for at least 10 minutes before serving.