If you want to export the roster events to your device calendar it can occur that you receive the following error message: "This account does not allow calendars to be added or removed".
You can resolve this error with the following steps:
1. Open the settings (iPhone menu)
2.Tap on your name (the first cell in Settings menu)
3. Go to iCloud section
4. Activate Calendar
Now you can export from RosterBuster App to your device calendar.