Update Parameters

My problem is that I can' t update my gridview. I am stuck at this problem for several days now and have no clue what the sollution could be. Hope somebody can give me some ideas of what I am doing wrong.

<asp:GridView ID="GridView_phl_berichten" runat="server" AutoGenerateColumns="False" BorderColor="DimGray" BorderStyle="Solid" BorderWidth="1px" DataKeyNames="phlb_id" DataSourceID="SqlDataSource_phl_berichten" GridLines="Horizontal" Width="716px">

<Columns>

<asp:TemplateField HeaderText="Van datum" SortExpression="phlb_van">

<EditItemTemplate>

&nbsp;<asp:Calendar ID="phlb_van" runat="server" SelectedDate='<%# eval("phlb_van") %>'

VisibleDate='<%# eval("phlb_van") %>'></asp:Calendar>

</EditItemTemplate>

<ItemStyle VerticalAlign="Top" Width="5cm" />

<ItemTemplate>

<asp:Label ID="Label_datum_van" runat="server" Text='<%# eval("phlb_van", "{0:d}") %>'></asp:Label>

<br />

<br />

<asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Edit"

Text="Edit"></asp:LinkButton>

<asp:LinkButton ID="LinkButton2" runat="server" CausesValidation="False" CommandName="Delete"

Text="Delete" OnClientClick=" return confirm('Bent u zeker dat u dit bericht wil verwijderen ?') "></asp:LinkButton>

</ItemTemplate>

</asp:TemplateField>

<asp:TemplateField HeaderText="Tot datum" SortExpression="phlb_tot">

<EditItemTemplate>

&nbsp;<asp:Calendar ID="phlb_tot" runat="server" SelectedDate='<%# eval("phlb_tot") %>'

VisibleDate='<%# eval("phlb_tot") %>'></asp:Calendar>

</EditItemTemplate>

<ItemStyle VerticalAlign="Top" Width="4cm" />

<ItemTemplate>

<asp:Label ID="Label_datum_tot" runat="server" Text='<%# eval("phlb_tot", "{0:d}") %>'></asp:Label>

</ItemTemplate>

</asp:TemplateField>

<asp:TemplateField HeaderText="Bericht" SortExpression="phlb_bericht">

<EditItemTemplate>

&nbsp;<asp:TextBox ID="phlb_bericht" runat="server" Height="98px" Text='<%# eval("phlb_bericht") %>'

TextMode="MultiLine" Width="527px"></asp:TextBox><br />

<br />

&nbsp; &nbsp;&nbsp;

<asp:LinkButton ID="LinkButtonUpdate" runat="server" CausesValidation="False" CommandName="Update"

Font-Size="Small" OnClientClick="return confirm('Bent u zeker dat u dit bericht wil opslaan ?')"

Text="Update"></asp:LinkButton>

&nbsp; &nbsp; &nbsp; &nbsp;

<asp:LinkButton ID="LinkButtonCancel" runat="server" CausesValidation="False" CommandName="Cancel"

Font-Size="Small" Text="Cancel"></asp:LinkButton>

</EditItemTemplate>

<ItemTemplate>

&nbsp;<asp:TextBox ID="TextBox_bericht" runat="server" Height="98px" ReadOnly="True"

Text='<%# eval("phlb_bericht") %>' TextMode="MultiLine" Width="527px"></asp:TextBox>

</ItemTemplate>

</asp:TemplateField>



<asp:TemplateField HeaderText="phlb_id" SortExpression="phlb_id" Visible="False">

<EditItemTemplate>

<asp:Label ID="phlb_id" runat="server" Text='<%# Bind("phlb_id") %>'></asp:Label>

</EditItemTemplate>

<ItemTemplate>

<asp:Label ID="Label_bericht_id" runat="server" Text='<%# Bind("phlb_id") %>'></asp:Label>

</ItemTemplate>

</asp:TemplateField>

</Columns>

<HeaderStyle BackColor="#F3F3F3" />

</asp:GridView>

and here is my sqldatasource-object :

<asp:SqlDataSource ID="SqlDataSource_phl_berichten" runat="server" ConnectionString="<%$ ConnectionStrings:ConEP %>"

SelectCommand="sp_berichten_PHL_alle" SelectCommandType="StoredProcedure" UpdateCommand="UPDATE T_bericht_PHL set&#13;&#10;phlb_bericht = @phlb_bericht &#13;&#10;where phlb_id = @phlb_id">

<UpdateParameters>

<asp:Parameter Name="phlb_bericht" Type="String" />

<asp:Parameter Name="phlb_id" Type="Int32" />

</UpdateParameters>

</asp:SqlDataSource>

It always stay giving the message that you can ' t insert null values in the column " bericht " ... ; All my variables have the same names as the columns in my table. So it is finding the id , but it doesn' t seem to find the value of my edititemtemplatefield "bericht". Hope somebody can give some suggestions on what I can try to do else.