Can anyone help me? thanks

Based on my test, you will need to set the datakeyfield of the grid during the PrepareDataBinding event handler, here is the snippet:

protected void WebGrid1_PrepareDataBinding(object sender, ISNet.WebUI.WebGrid.DataSourceEventArgs e)
{
    WebGrid1.RootTable.DataKeyField = "id";
    WebGrid1.RetrieveStructure();
    WebGrid1.RootTable.DataKeyField = "id";
}

You will also need to re-set the command during batch update event handler and invoke the RefreshAll client side method, here is the snippet:

protected void WebGrid1_BatchUpdate(object sender, ISNet.WebUI.WebGrid.BatchUpdateEventArgs e)
{
    DataSet dt = (DataSet)WebGrid1.GetCachedDataSource();
    DataSet changeDT = (DataSet)dt.GetChanges();

    da = new SqlDataAdapter("SELECT  * FROM logintbl;", conn);
    SqlCommandBuilder builder = new SqlCommandBuilder(da);

    da.InsertCommand = builder.GetInsertCommand();
    da.UpdateCommand = builder.GetUpdateCommand();
    da.DeleteCommand = builder.GetDeleteCommand();

    da.Update(changeDT);
    WebGrid1.ClientAction.RefreshAll();
}

thankyou