germanero on "[Plugin: Simple Calendar - Google Calendar Plugin] Works Fine but can't select an date interval"

It's ok, but when I choose some period of time, like: start on 9/23/16 and ends on 9/25/16 the calendar doesn't display anything. So, you must to update and fix this problem.
Regards.

https://wordpress.org/plugins/google-calendar-events/

Do you have a link to the page so I can check it out?

What are your other calendar settings?

Also, please run through this to make sure there is nothing conflicting: http://docs.simplecalendar.io/troubleshooting-theme-plugin-widget-conflicts/

The calendar settings is default. Just select list mode, then I followed all steps (step by step from advanced) where you give some instructions to configure calendar from google. I bought a template (Archtek) and then install simple Calendar, then just choose list mode, set api and calendar code from my new calendar on calendar.google.com. When I use one day to the event all is fine. The problem is when you choose some days (date to date) this event day not showing (only single event days), just disappear. So I have to go back and choose one single day. Is the only issue I have.
I'm not using cache plugins, only the simple calendar cache system. In your demo site the lists only shows single day, but doesn't show when you set some days and scheduler options...
Best regards.