Intenta buscando en tu código
Insertar CODE, HTML o PHP:
<b:includable id='commentForm' var='post'> </b:includable>
y todo lo que este dentro reemplazalo por
Insertar CODE, HTML o PHP:
<div class='comment-form'>
<a name='comment-form'/>
<h4 id='comment-post-message'><data:messages.postAComment/></h4>
<b:if cond='data:this.messages.blogComment != ""'>
<p><data:this.messages.blogComment/></p>
</b:if>
<b:include data='post' name='commentFormIframeSrc'/>
<iframe allowtransparency='allowtransparency' class='blogger-iframe-colorize blogger-comment-from-post' expr:height='data:cmtIframeInitialHeight ?: "90px"' frameborder='0' id='comment-editor' name='comment-editor' src='' width='100%'/>
<data:post.cmtfpIframe/>
<script type='text/javascript'>
BLOG_CMT_createIframe('<data:post.appRpcRelayPath/>');
</script>
</div>
Solo para probar xd (puede que le falte css)