Web Player always reinstall on IE

Hi, i built a wp player of a project and hosted it on a server. With IE everytime I open that page it asks me to reinstall the player like the very first time (with the "get unity" png logo). Could it be a problem related to customized myproject.html page? here is the code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

    Unity Web Player | TPTstreamed
};

    if (typeof unityObject != "undefined") {
        unityObject.embedUnity("unityPlayer", "Contenuti/TPTstreamed.unity3d", 800, 600, params);
    }
    -->
    </script>
    <style type="text/css">
    <!--
    body {
        font-family: Helvetica, Verdana, Arial, sans-serif;
        background-color: black;
        color: white;
        text-align: center;
    }
    a:link, a:visited {
        color: #bfbfbf;
    }
    a:active, a:hover {
        color: #bfbfbf;
    }
    p.header {
        font-size: small;
    }
    p.header1 {
        font-size: big;
        font-weight: bold;
    }

    p.header span {
        font-weight: bold;
    }
    p.footer {
        font-size: x-small;
    }
    div.content {
        margin: auto;
        width: 800px;
    }
    div.missing {
        margin: auto;
        position: relative;
        top: 50%;
        width: 193px;
    }
    div.missing a {
        height: 63px;
        position: relative;
        top: -31px;
    }
    div.missing img {
        border-width: 0px;
    }
    div#unityPlayer {
        cursor: default;
        height: 600px;
        width: 800px;
    }
    -->
    </style>
</head>
<body>
    <p class="header"><span></span>Area Marina Protetta</p>
    <p class="header1"><span></span>Secche di Tor Paterno</p>
    <div class="content">
        <div id="unityPlayer">
            <div class="missing">
                <a href="http://unity3d.com/webplayer/" title="Unity Web Player. Install now!">
                    <img alt="Unity Web Player. Install now!" src="http://webplayer.unity3d.com/installation/getunity.png" width="193" height="63" />
                </a>
            </div>
        </div>
    </div>
    <p class="footer"><a href="http://ubicasrl.com" title="Go to unity3d.com">UBICA srl</a></p>
</body>

This happened to me, I had to allow the add-on in the add on manager.