Apple requires all third-party apps that sync with iCloud (like BusyCal and BusyContacts) to use app-specific passwords. An app-specific password is essentially a custom password that is different than your standard iCloud password. Only Apple's apps (Mail, Calendar and Contacts) can use your standard iCloud password. All other apps must use an app-specific password to connect with your iCloud account.
If you are syncing BusyCal or BusyContacts with iCloud, please follow these instructions for using an app-specific password in BusyCal and BusyContacts.
Please contact us if you have questions.