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How can I link gallery thumbnails to actual post?

You can link gallery thumbnail to the actual post by replacing this code in common-functions.php, ( line 300 )

elseif($thumb_url != '') {
   $output = '<a href="'.$thumb_url[0]. '"rel="cb-image" class="cb-single">'.$thumb.'</a>';
}

with this:

elseif($thumb_url != '') {
   $output = '<a href="'.get_permalink($postid).'">'.$thumb.'</a>';
}