This works on Android. Go to settings, Apps, manage apps. Scroll down to Fitbit and click it. At the bottom of the screen it says, Force stop, uninstall and Clear Data. Click on Clear Data, two new options appear. Clear All Data and Clear Cache. For now ignore Clear All Data, but click on Clear Cache. Close settings and then try connecting to your device again. This will not affect any data your fitbit has recorded, so you don't lose anything. 90% of the time this corrects the problem
