In my form I have a textbox and a calendr along with other controls

asp:TextBox ID="TextBox2" runat="server" onfocus="CalOpen()" asp:TextBox>

asp:Calendar ID="Calendar1" runat="server" style="display:none;" onselectionchanged="Calendar1_SelectionChanged">

script type="text/javascript">

    function CalOpen()
    {
     var cal = document.getElementById('<%=Calendar1.ClientID%>');
     cal.style.display='block';

    }

/script>

protected void Calendar1_SelectionChanged(object sender, EventArgs e)

{
    TextBox2.Text = Calendar1.SelectedDate.ToLongDateString();
    Calendar1.Visible = false;
}


protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
    Calendar1.Visible = true;
}

For the first time it worked fine, but, 2nd time when I click TextBox2, that is, after selecting date for the first time. Broeser is throwing error"object required"

I am unable to know where I went wrong.

Plz help me in making my code correct.

Thank You.