dayvead on "Duplicate Theme Fatal Error"

Good afternoon,

I've duplicated a theme and done what is written in the next tutorial : http://www.zenphoto.org/news/theming-tutorial

And also changed the name of the previous theme in each php files where it appears .

But i've the next error message :
" Fatal error: Call to a member function theme_head() on a non-object in /www/***/themes/Sunny/album.php on line 14 "

Thanks a lot anyone for replying.