[Plugin: NextGEN Gallery] Plug in check error msg

I am using Gallery 1.9.3, smooth 1.2, theme Atahualpa 3.7.3, my URL is buckchucko.com

When I did the plug in check, I got the following error. How to fix?

Missing the call to wp_head() in your theme, contact the theme author

Thanks

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/