Secondary objectives: 1) To establish the tolerability and safety of Quetiapine XR versus Placebo in patients with co-morbid depressive and anxiety disorders;2) To assess and compare the efficacy of Quetiapine XR versus Placebo improving quality of life in patients with co-morbid depressive and anxiety disorders.; 3) To assess and compare the efficacy of Quetiapine XR versus Placebo on clinical measures symptoms associated to co-morbid depressive and anxiety disorders.