Insert statement does not insert any data - asp.net

Question

I have a page where I display a list of groups for my application. There can be multiple users in a group. The group list is implemented with a gridview. Besides the column for the group description, the gridview has a button for adding users to it. When I click this button, the groupid is passed to a new page, on this page there is another gridview with a list of users. The gridview also has a buttonfield for adding that specific user to the group's group id. For this I have an extra table:
UserGroup
usergroupid
userid
groupid
My problem is, nothing is inserted into this table, the insert command is executed but something seems to be missing.
Here is my code:
Markup:
<asp:Content ID="content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<asp:GridView OnRowCommand="grdBenutzer_RowCommand" ID="grdBenutzer" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1">
<Columns>
<asp:BoundField ReadOnly="true" DataField="BenutzerID" HeaderText="ID" />
<asp:TemplateField HeaderText="Bezeichnung">
<ItemTemplate>
<%# Eval("Bezeichnung")%>
</ItemTemplate>
<EditItemTemplate>
<asp:DropDownList AppendDataBoundItems="true" runat="server" ID="ddwnBezeichnung" Text='<%# Bind("Bezeichnung")%>'>
<asp:ListItem Text="Mitarbeiter" Value="Mitarbeiter"></asp:ListItem>
<asp:ListItem Text="Praktikant" Value="Praktikant"></asp:ListItem>
<asp:ListItem Text="Azubi" Value="Azubi"></asp:ListItem>
<asp:ListItem Text="Umschüler" Value="Umschüler"></asp:ListItem>
</asp:DropDownList>
</EditItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Vorname">
<ItemTemplate>
<%# Eval("Vorname")%>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox runat="server" ID="txtVorname" Text='<%# Bind("Vorname")%>' />
</EditItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Nachname">
<ItemTemplate>
<%# Eval("Nachname")%>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox runat="server" ID="txtNachname" Text='<%# Bind("Nachname")%>' />
</EditItemTemplate>
</asp:TemplateField>
<asp:BoundField ReadOnly="true" HeaderText="Geburtsdatum" DataField="Geburtsdatum" />
<asp:TemplateField HeaderText="Benutzerart">
<ItemTemplate>
<%# Eval("Benutzerart")%>
</ItemTemplate>
</asp:TemplateField>
<asp:ButtonField ButtonType="Button" HeaderText="Mitglied hinzufügen" Text="Mitglied hinzufügen" CommandName="MitgliedHinzufuegen" />
</Columns>
</asp:GridView>
<asp:SqlDataSource OnInserted="SqlDataSource1_Inserted" ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT [BenutzerID], [Bezeichnung], [Vorname], [Geburtsdatum], [Nachname], [Benutzerart] FROM [Benutzer] WHERE [Archiviert] != 1"
InsertCommand="INSERT INTO BenutzerGruppe (BenutzerID, GruppenID) VALUES (#BenutzerID, #GruppenID)">
</asp:SqlDataSource>
</asp:Content>
Code-behind:
protected void SqlDataSource1_Inserted(object sender, SqlDataSourceStatusEventArgs e)
{
Response.Redirect("Gruppenverwaltung.aspx");
}
protected void grdBenutzer_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "MitgliedHinzufuegen")
{
string gruppenid = Request.QueryString["GruppenID"];
SqlDataSource1.InsertParameters.Add("GruppenID", gruppenid);
SqlDataSource1.Insert();
}
}
The inserted method fires after I add an user to the group, but when I view the group's members, no user was added....

Answer 1

The insert command expects input parameter #BenutzerID which you don't appear to be providing in the code-behind.