Need Help With Update Link In FormView - URGENT

Hi Folks,

 Somehow i am stuck at a very basic step. I have two pages  -

1. DomainList.aspx which just displays all the records from the Domains table.
2. DomainAddEdit.aspx which displays the selected record in FormView(Edit Mode) with two link for Update and Cancel.

The Update link in the FormView does nothing on the first click. It just reloads the page with the new data I entered. If I click again on the Update link, it throws me an error:

"Cannot insert the value NULL into column 'DNS', table 'MSInteractive.dbo.Domains'; column does not allow nulls. UPDATE fails.
The statement has been terminated. "

I have no clue why all this is happening. I have spent more than two days on this and this is very very frustrating.

Just to mention, I haven't written any code for this. Its developed all using the VWD tools available. I have posted this message earlier but haven't got any response. I am sure most of you guys must have been doing these steps everyday. So, please post your thoughts.

 Thanks a million.

Here is the relevant code for my DomainADDEdit.aspx:

<asp:FormView ID="FormView1" runat="server" DataSourceID="SqlDataSource1" DefaultMode="Edit">
        <EditItemTemplate>
            Id:
            <asp:TextBox ID="IdTextBox" runat="server" Text='<%# Bind("Id") %>'></asp:TextBox><br />
            RegistrarAccountId:
            <asp:TextBox ID="RegistrarAccountIdTextBox" runat="server" Text='<%# Bind("RegistrarAccountId") %>'></asp:TextBox><br />
            Registrar:
            <asp:TextBox ID="RegistrarTextBox" runat="server" Text='<%# Bind("Registrar") %>'></asp:TextBox><br />
            DNS:
            <asp:TextBox ID="DNSTextBox" runat="server" AutoPostBack="True" OnTextChanged="DNSTextBox_TextChanged"
                Text='<%# Bind("DNS") %>'></asp:TextBox><br />
            EmailHost:
            <asp:TextBox ID="EmailHostTextBox" runat="server" Text='<%# Bind("EmailHost") %>'></asp:TextBox><br />
            Registered:
            <asp:TextBox ID="RegisteredTextBox" runat="server" Text='<%# Bind("Registered") %>'></asp:TextBox><br />
            Expires:
            <asp:TextBox ID="ExpiresTextBox" runat="server" Text='<%# Bind("Expires") %>'></asp:TextBox><br />
            MsiResponsible:
            <asp:CheckBox ID="MsiResponsibleCheckBox" runat="server" Checked='<%# Bind("MsiResponsible") %>' />
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:MSInteractiveConnectionString %>"
        SelectCommand="SELECT [Id], [RegistrarAccountId], [Registrar], [DNS], [EmailHost], [Registered], [Expires], [MsiResponsible] FROM [Domains] WHERE ([Id] = @Id)"
        UpdateCommand="UPDATE Domains SET DNS = @txtDNS WHERE (Id = @Id)">
        <UpdateParameters>
            <asp:FormParameter FormField="DNSTextBox" Name="txtDNS" />
            <asp:QueryStringParameter Name="Id" QueryStringField="Id" />
        </UpdateParameters>
        <SelectParameters>
            <asp:QueryStringParameter Name="Id" QueryStringField="Id" Type="String" />
        </SelectParameters>
    </asp:SqlDataSource>
<br />
            <asp:LinkButton ID="UpdateButton" runat="server" CommandName="Update"
                Text="Update" OnClick="UpdateButton_Click"></asp:LinkButton>
            <asp:LinkButton ID="UpdateCancelButton" runat="server" CausesValidation="False" CommandName="Cancel"
                Text="Cancel"></asp:LinkButton>
        </EditItemTemplate>