In order to post a picture to your story, you need to make sure that you are using a stable Internet connection. The behavior that you encounter could be caused by a network issue. You should check that first. Also, you can go to the Menu of your device > Settings > Applications > Manage Applications > All tab, search for Snapchat and tap on it. From there, tap on Clear Cache. After you did this, open the application and try to post the picture again. You shouldn't encounter any more problems.
