Weird nextpage problem

I’m using a theme called SEO-Red that includes in page.php the exact same nextpage code as the WordPress Default theme:

<?php wp_link_pages(array(‘before’ => ‘<p>Pages: ‘, ‘after’ => ‘</p>’, ‘next_or_number’ => ‘number’)); ?>

It works fine, of course, in the Default theme. However, when I switch to SEO-Red – it no longer works.

Does anyone have a clue as to where I might start looking for the answer to this riddle? Thanks!