$_POST trouble with html form

Why am I getting the error "Undefined index: comment"? It's probably a typo because I had something similar that worked. <form action="<?php include (ACTION_DIR."/jpeg-comment.php"); ?>" method="post">

    <textarea name="comment" ROWS=6 COLS=60>
      <?php print $comments[$thumb_num] ?>
    </textarea><br>
    <input type="submit" value="update annotation">

</form>

    <?php
    echo $_POST["comment"]; # this is just for debugging
    ?>

Also perhaps related, when I call $_POST["comment"] in the action file, it gives me "Forbidden You don't have permission to access...[error message]" but this is my own server at home. I'm quite unfamiliar with forms (and new to PHP for that matter).