Reply To: Error: Missing required field "entry-title"

After a little bit of digging I found the fix. Just a slight modification to the code:

//mod content
function hatom_mod_post_content ($content) {
  if ( in_the_loop() && !is_page() ) {
    $content = '<span class="entry-content">'.$content.'</span>';
  }
  return $content;
}
add_filter( 'the_content', 'hatom_mod_post_content');

//add hatom data
function add_mod_hatom_data($content) {
    $t = get_the_modified_time('F jS, Y');
    $author = get_the_author();
    $title = get_the_title();
    if ( is_single() || is_page()) {
        $content .= '<div class="hatom-extra" style="display:none;visibility:hidden;"><<span class="entry-title">'.$title.'</span> was last modified: <span class="updated"> '.$t.'</span> by <span class="author vcard"><span class="fn">'.$author.'</span></span></div>';
    }
    return $content;
    }
add_filter('the_content', 'add_mod_hatom_data');

In any case, it’s obvious that this problem is not in any way related to Connections-Pro and is instead a widespread WordPress problem – so your assistance in resolving it was above and beyond anything anyone could expect of you, and just one more reason why I can’t recommend this plugin to anyone interested in purchasing it enough.