This error occurs when the app doesn't have the appropriate permissions to your Fitbit profile. Please do the following.
- Log into you Fitbit.com account using your web browser.
- Click on your profile icon at the top right of your screen
- Click on the watch at the top right of your screen
- Scroll down on the left at the bottom you should see "Applications". Click on it.
- Scroll through the list and find "myFitnessSync by Bickster LLC"
- Click "Revoke Access"
- Launch our App again. Go to Settings and click "Logout"
- Click "Login". Make sure to keep "profile" checked along with the other fields.