Thickbox error on Atahualpa theme when using crossword plugin

I am trying to add a crossword puzzle to my website (http://new.michiganbees.org/2011/08/...ssword-puzzle/) using the Eclipse crossword puzzle plugin. It works fine on another theme, but when I switch to the atahualpa theme I get this message:
"Object doesn't support this property or method
thickbox.js"

Do you know why it won't work with your theme and is there a way to make it work?
Thanks for your help.