C# – A potentially dangerous Request.Form value was detected from the client

When I try to post any thing that contains <whatever> I get

A potentially dangerous Request.Form
value was detected from the client
Description: Request Validation has
detected a potentially dangerous
client input value, and processing of
the request has been aborted. This
value may indicate an attempt to
compromise the security of your
application, such as a cross-site
scripting attack. To allow pages to
override application request
validation settings, set the
requestValidationMode attribute in the
httpRuntime configuration section to
requestValidationMode="2.0". Example:
. After
setting this value, you can then
disable request validation by setting
validateRequest="false" in the Page
directive or in the
configuration section. However, it is
strongly recommended that your
application explicitly check all
inputs in this case. For more
information, see
http://go.microsoft.com/fwlink/?LinkId=153133.

Exception Details:
System.Web.HttpRequestValidationException:
A potentially dangerous Request.Form
value was detected from the client

I have following asp.net code

 <asp:DetailsView ID="newsDetail" runat="server" DataSourceID="SqlDataSourceNews"
                AutoGenerateRows="False" DataKeyNames="id" 
                OnItemUpdating="NewsDetailItemUpdating" OnItemCreated="NewsDetailItemCreated"
                OnItemDeleted="NewsDetailItemDeleted" OnItemInserted="NewsDetailItemInserted"
                OnItemInserting="NewsDetailItemInserting" OnItemUpdated="NewsDetailItemUpdated"
                DefaultMode="Insert">

                <Fields>
                    <asp:TemplateField FooterText="show at statpage" HeaderText="view" SortExpression="view">
                       ...
                    </asp:TemplateField>
                    <asp:BoundField DataField="headline" HeaderText="Headline" SortExpression="headline">
                    </asp:BoundField>
                    <asp:TemplateField HeaderText="Text">
                        <ItemTemplate>
                            <asp:Label ID="post" runat="Server" Text='<%# Eval("post") %>' OnPreRender="PostLabelPreRender" />
                        </ItemTemplate>
                        <InsertItemTemplate>
                            <asp:TextBox ID="postTextBox" runat="server" Text='<%# Bind("post") %>' TextMode="MultiLine"
                                Width="500px" Height="300px" />
                        </InsertItemTemplate>
                        <EditItemTemplate>
                            <asp:TextBox ID="postTextBox" runat="server" Text='<%# Bind("post") %>' TextMode="MultiLine"
                                Width="500px" Height="300px" />
                        </EditItemTemplate>
                    </asp:TemplateField>

And the code

    protected void NewsDetailItemUpdating(object sender, DetailsViewUpdateEventArgs e)
    {
        // Iterate though the values entered by the user and HTML encode 
        // the values. This helps prevent malicious values from being 
        // stored in the data source.
        for (int i = 0; i < e.NewValues.Count; i++)
            if (e.NewValues[i] != null)
                e.NewValues[i] = Server.HtmlEncode(e.NewValues[i].ToString());
    }

    protected void NewsDetailItemInserting(object sender, DetailsViewInsertEventArgs e)
    {
        for (int i = 0; i < e.Values.Count; i++)
            if (e.Values[i] != null)
                e.Values[i] = Server.HtmlEncode(e.Values[i].ToString());
    }

    protected void NewsDetailItemUpdated(object sender, DetailsViewUpdatedEventArgs e)
    {
        newsList.DataBind();
    }

    protected void NewsDetailItemInserted(object sender, DetailsViewInsertedEventArgs e)
    {
        newsList.DataBind();
    }

    protected void NewsDetailItemDeleted(object sender, DetailsViewDeletedEventArgs e)
    {
        newsList.DataBind();
    }

    protected void NewsDetailItemCreated(object sender, EventArgs e)
    {
        newsList.DataBind();
    }