Your theme is using old and deprecated function link_pages
to display page-links for paginated posts.
Just replace this chunk of code:
<div class="pagelink"><?php wp_link_pages('pagelink=Source %'); ?></div>
<div class="format_text">
<?php the_content('<p>Read the rest of this entry »</p>'); ?>
<?php link_pages('<p><strong>Pages:</strong> ', '</p>', 'number'); ?>
</div>
with this:
<div class="format_text">
<?php the_content('<p>Read the rest of this entry »</p>'); ?>
<?php wp_link_pages( array( 'before' => '<div class="page-link">Pages:', 'after' => '</div>', 'pagelink' => 'Source %' ) ); ?>
</div>