This is an open label, single arm phase II study of BKM120 in men with metastatic castration resistant prostate cancer (CRPC) who have progressed on or following completion of docetaxel-based chemotherapy. Prior progression on cabazitaxel, provenge, abiraterone, or enzalutamide (MDV3100) is also permitted. Patients must have baseline evaluations performed prior to the first dose of study drug and must meet all inclusion and exclusion criteria. Results of the baseline evaluations, which assure that all inclusion and exclusion criteria have been satisfied, must be reviewed by the Principal Investigator or his/her designee prior to enrollment of that patient. In addition, the patient must be thoroughly informed about all aspects of the study, including the study visit schedule and required evaluations and all regulatory requirements for informed consent. The written informed consent must be obtained from the patient prior to protocol-specific screening tests. The following criteria apply to all patients enrolled onto the study unless otherwise specified.