First try shutting down your phone and turning it back on. If that doesn't work, try re-installing the application. According to Sprint, when other things don't seem to work or your phone freezes up, doing a battery pull will reset the phone's memory and cause it to work again. To do a battery pull, shut the phone power off, take the battery out and count to 30 seconds. Then reinstall the battery and power the phone back up. This has helped me in the past.