MVC2 Ajax Form does unwanted page refresh

I am pretty new to MVC. I have my first Ajax Form here:

<div id="test"></div>
<div id="MainChatMenu">
<% using (Ajax.BeginForm("SendMessage", "MainChat", new AjaxOptions {  UpdateTargetId="test"}))
{ %>
  <input id="chatMessageText" type="text" maxlength="200"  />
<input type="submit" value="Go"/>
<% } %>

Now, if I click the submit button, the page is reloading, goint to mysite/controller/action. I thought that the default behaviour of the Ajax.BeginForm was exactly not to do that? Where's my newbie mistake?

My Controller is called correctly, but data passing also doesn't work. Probably because of the same mistake? Here's the code:

public class MainChatController : Controller
{
    [AcceptVe开发者_Go百科rbs(HttpVerbs.Post)]
    public EmptyResult SendMessage(FormCollection formValues)
    {
        return new EmptyResult();
    }

}

Make sure you have included the necessary script libraries:

<script type="text/javascript" src="<%= Url.Content("~/scripts/MicrosoftAjax.js") %>"></script>
<script type="text/javascript" src="<%= Url.Content("~/scripts/MicrosoftMvcAjax.js") %>"></script>

<% using (Ajax.BeginForm("SendMessage", "MainChat", new{}, new AjaxOptions {  UpdateTargetId="test", HttpMethod="POST"})) %>