Hello Christian Eichert,

By default openerp set the field "secrets path" with value as a "client_secrets.json". But there was no file, we need to provide file name with path where JSON file located.

You can create and download json file from "console.developers.google.com". First create a new project and go to the “APIS & AUTH/ APIs” section. Enable “calendar API”.

Now go to the “Credentials” just below the APIs section of your project and click on “Download JSON" and save this file on a location where your Odoo/OpenERP system has access to it. 

In “Secrets path” enter the full path of downloaded json file/ (example: /home/openerp/google_calendar/client_secrets.json).

Enter path for “Credential path” field. When we authorize, google_api will create the credential file and fill data. (example: /home/openerp/google_calendar/credentials.dat). File should have read and write access.