asp.net calendar control

I add a simple calendar control in my asp.net page, but i can't change month. Links prev/next month don't work ...

<form runat="server">
<asp:Calendar ID="Calendar1" runat="server" BorderStyle="Double" Bo开发者_JAVA技巧rderWidth="3px"
    DayNameFormat="FirstTwoLetters" FirstDayOfWeek="Monday" ShowGridLines="True" 
    NextPrevFormat="ShortMonth"
    CellPadding="0"  
    OnDayRender="Calendar1_DayRender" >
    <OtherMonthDayStyle ForeColor="LightGray"></OtherMonthDayStyle>
</asp:Calendar>
</form>

Help please ^^ thank's

P.S. It's not a date picker, it's an event calendar ...

What is your Calendar1_DayRender code look like? Are you trying to set a default date? If so, are you only doing it if !IsPostBack ? I put this code in a test page and it works just fine.