GCal integration with Appointments+ doesn't do anything

Hi there.

I'm running Wordpress 3.5.1 and Appointments+ 1.2.8. I'm trying to get the GCal API integration to work. I followed the setup instructions on the GCal settings page within Appointments+ to the letter. There were no problems, except that when I saved my new calendar, I was asked whether or not to invite the user x@developer.gserviceaccount.com to Google Calendar, where x is my particular account name, obtained as per the setup instructions. Whether or not I choose to invite the 'new' user to GCal, nothing works. Click on the 'Test Connection' button within GCal just reloads the Appointments+ GCal tab without giving any output. Nothing propagates to my GCal. I have tried synchronization in both directions, using both synchronization settings. Nothing is happening and there are no error messages.

Your help would be appreciated.