popup image boxes any help is poss

[Alxb]

i have as far as i know installed everything correctly how ever when i try to view a larger version of a product i get this

 

" Fatal error: Failed opening required 'catalog/includes/application_top.php' (include_path='.:/usr/local/php-4.2.3/lib/php') "

 

in the resized pop up window. the line that triggers this is

" /catalog/popup_image.php on line 13"

 

does anyone have an idea about this

 

Thanks