[Plugin: Ajax Event Calendar] I can't delete the default categories

Hi ! I’m very disappointed because the plugin works very well except that I can’t change or delete the default preset categories ! So it’s impossible to use the calendar ! Look at the agenda page here : http://wp.artistic-online.com

I can add new ones but when I click to delete or update the created ones, a blank page appears.

http://wordpress.org/extend/plugins/ajax-event-calendar/