The study will consist of a Screening period (7 to 21 (±3) days) from Visit 1 to Visit 2, followed by a Single-blind Placebo Run-in period (7 to 10 days) from Visit 2 to Visit 3, followed by a 6-month (26 weeks) double-blind treatment period (Visit 3 through Visit 11). Subjects who complete this study will be allowed to participate in a 6-month open-label extension study (Study 060-635).