I am a newbee of .NET C#. I've coded as below:

<form action="second.aspx" method="post">
  <P>What Martial Art do you like?
    <asp:radiobuttonlist id="radio1" runat="server">
        <asp:listitem value="Capoeira"/>
        <asp:listitem value="Shaolin"/>
        <asp:listitem value="JKD"/>
    </asp:radiobuttonlist>
  </P>
  <P><input type="submit" value="Submit"></P>
</form>

According to "Beginning ASP.NET using C#" page 131 said, no need to put "runat=server" at "<form>", but the page totally can't be loaded and errors have come out: "Control 'radio1_0' of type 'RadioButton' must be placed inside a form tag with runat=server."...

Could anyone tell me what's wrong?

Server controls have to be inside a form with runat="server". On the other hand, if you are using only HTML (client Side) controls, ruat="server" is not needed. There can be only one form in a page with runat="server".

Regards
Ganesh