After installing the plugin, and setting up a "public" Google Calendar in my Gmail account, this is the error message I get in my site:
1 or more of your feeds could not be displayed. The following errors occurred:
Feed 1: Access to this feed was denied (403). Please ensure you have public sharing enabled for your calendar.
I made sure that the Google Calendar is public. I'm also using this shortcode within the WP Editor:
[google-calendar-events id="1" type="ajax" title="Events on" max="25"]
Any ideas why the feed can't be read?