comments_template in a template

Hello all. I am porting an application from a joomla to wordpress. I have created a template, including my app. And created a page with that template. It works fine. That page is suppose to have a possible comment. I have checked the comment in the page edition. In my template, I have included the 2 magik lines:

$withcomments = true;
comments_template();

I can type a comment, but, when I validate, i have a blank wp-comment-post.php page. In my sources, i have:

<input type="hidden" name="comment_post_ID" value="" />

with no value to comment_post_ID. I dontsee how to correct this.
Any help ?

Thanks.