[Plugin: The Events Calendar] category month view no show, but month in URL does

The Events Calendar has been working fine, until recently.
now nothing will show up when the URL is just category, it only shows up when the specific month is in the URL string.

Example:
http://aslinsideatl.com/category/events/

vs.
http://aslinsideatl.com/category/events/2010-03/

http://wordpress.org/extend/plugins/the-events-calendar/