Some Google Apps accounts do not automatically have the setting for private calendar sharing, you will need to enable this to access a private ICS feed for your Calendar. For the protection of your privacy and the privacy of your clients, we highly recommend keeping your Google Calendar private.
- Login to your Google Apps Admin console and go to the Settings of your account.
- Select Manage this domain.
- Go to Apps, Google Apps and then Calendar.
- Under Sharing settings, select either Share all information, and outsiders can change calendars or Share all information, and allow managing of calendars.
- Click Save.