Back in November 2011, we announced the deprecation of the Calendar GData API (v1, v2) when theAPIv3 was made available. We’ll now be shutting down these older versions on November 17, 2014.
Any service dependent on the Calendar GData API (v1, v2), such as the Google Calendar Connectors (GCC), will no longer work as intended. GCC users should update to use Calendar Interop or their own custom built connectors that sync with v3 of the API.
Reference by : www.google.com