Widget breaking my theme

I have had this plugin installed but only last week it broke my theme but only when I activate the sidebar widget.

The site is www.cosst.org.uk

Why has it done this?

Screenshot with error

Screenshot without widget

I see the images are to large to show the error fully so here are some links to the images



It w’d be great to have a page with scheduler widget.
You might turn on widget, save this page using your browser and send me package with all necessary files.