Asp.net ASP:Login and forms - asp.net

Question

On my webpage, I use ASP:Login, when members login to my page, very standard.
I also have a contact-form.
When I use my contact-form, there is no problem, but when I log in as a member, at use the contact form, nothing gets submitted, but the "form page" just loads again.
If I then fill out the form again, and hit the submit-button, the information is send.
My form is build like this:
<asp:Panel id="NameSug" Runat="server" DefaultButton="SendSug">
<asp:Textbox name="NavnForslag" id="NavnForslag" runat="server" width="200" MaxLength="18" /><br/><br/>
<asp:imagebutton id="SendSug" onclick="CupName_click" runat="server" ImageUrl="images/login.gif"/>
</asp:Panel>
So if I'm not logged in, and fill out the form, it sends right away. If I'm logged in, I have to hit the "send" button, fill out the form again, and hit send again.
My backend-file looks like this:
public partial class usercontrols_msgSystem_CupNameSugFront : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
// Do something
}
protected void CupName_click(object sender, ImageClickEventArgs e)
{
// Do something else
}
}
My overall form-tag (I have one, that "surrounds" all the forms), looks like this:
<form id="DasTeam" runat="server">
Also, my login-form looks like this:
<asp:Login id="Login1" runat="server" DestinationPageUrl="~/Login.aspx">
<LayoutTemplate>
<div id="login">
<asp:Panel ID="panelLogin" runat="server" DefaultButton="submitLoginBtn">
<p class="tekst_alias">Alias:</p>
<p class="box"><asp:TextBox ID="UserName" runat="server" Width="150px"></asp:TextBox></p>
<p class="tekst"> Password:</p>
<p class="box"><asp:TextBox ID="Password" runat="server" TextMode="Password" Width="150px"></asp:TextBox></p>
<p class="login"><asp:LinkButton ID="submitLoginBtn" CommandName="Login" runat="server" CssClass="loginbutton">Login</asp:LinkButton></p>
<p class="failure"><asp:Literal ID="FailureText" runat="server" EnableViewState="False"></asp:Literal></p>
</asp:Panel>