Strange error on comment page

Hello. I thought I had everything up and running earlier thanks to some help from some of the kind members of the board earlier today but i seem to have stumpled upon another problem.

Basically instead of displaying a comment i am being shown his message:

Warning: call_user_func(scrapbook_comment) [function.call-user-func]: First argument is expected to be a valid callback in /home/millersa/public_html/scrapbook/wp-includes/comment-template.php on line 1335

you can see it in action for yourself here:
http://millersandlong.com/scrapbook/?p=1#comments

any advice is appreciated.

thanks.