MySqli_error

Lieta taada ka njemos ar viesu graamatas izveidi(primitiivas viesu graamatas). Atradu vienu skriptu no video tutoriaalja. Probleema ir tajaa ka informaacija no laukiem netiek ievietota datubaazee un taa vietaa paraadaas:
"Warning: mysqli_error() expects exactly 1 parameter, 0 given in G:\www\guestbook.php on line 17"

un veelviens error kas paraadaas jau atverot lapu:
"
Notice: Undefined index: txt_name in G:\www\guestbook.php on line 7"

Reku skripts:

<?
require($_SERVER["DOCUMENT_ROOT"]."/config/db_config.php");
       $connection = mysqli_connect($db_host, $db_user, $db_password) or die ("error connecting");
       $link = mysqli_connect($db_host, $db_user, $db_password, $db_name);
       mysqli_select_db($link, "weblapa");

       $name = $_POST["txt_name"];
       $len = strlen($name);
       if ($len > 0)
       {
$email = $_POST["txt_email"];
           $comment = $_POST["txt_comment"];
           $date = time();

           $query = "INSTER INTO guestbook (autoID, name, email, comment, date_auto) VALUES (NULL, '$name', '$email', '$comment', '$date')";
           <b> mysqli_query($link, $query) or die (mysqli_error()); </b>
}
?>
<html>

<head>
  <title>Guestbook</title>
</head>
<body>
<center>
<form action="<? echo $_SERVER['PHP_SELF']; ?>" method="POST">
<font face="arial" size="1">
    Name: <input type="text" name="txt_name">&nbsp;
        Email: <input type="text" name="txt_email"><br><br>
        Comment:<br>
        <textarea style="width: 75%" rows="10" name="txt_comment"></textarea>
               <center><input type="submit" value="Submit"></center>
</form>
</center>

</body>

</html>

Vai kaadam ir nojauta kaa panaak lai shis te straadaatu???