Great plugin! We've been using it for about a year now.
The website I help manage - http://montessorihouseforchildren.com/ - uses the calendar plugin as a sidebar widget and recently it was reported that users can't see events in months that are not the current month.
I've read through the last five pages of the support forum here and can't find any advice that helps me.
I have the "- ajax" option selected in the widget options.
I have W3 Total Cache installed and running, as well as APC cache on the server.
It appears to work in Chrome, when I am logged into WordPress. Logged out on all other browsers, and Chrome too, it does not work.