I have both the ImageGallery and EventCalendar modules installed. For my site, I placed the calendar on the sidebar so it is displayed on all the pages. When I visit my image gallery page, the calendar doesn't load or isn't shown.
The problem is that there are concurrent instances of jQuery being loaded. EventCalendar is using its own, while ImageGallery is using the jsparty source. I have updated the repository with the changes that should resolve your problem.
CalendarEvent, line 66
CalendarWidget.ss, line 1