For some reason I was having some value as null

Resolved it

Thank you so much for your help

I modified code and now I have

        <converter:GroupByValueConverter x:Key="GroupByValueConverter" ViewModel="{Binding ElementName=LayoutRoot,Path=DataContext.view1s}"></converter:GroupByValueConverter>

<ig:TemplateColumn.GroupByItemTemplate>
                        <DataTemplate>
                                <StackPanel Orientation="Horizontal">                                   
                                <TextBlock  Text="{Binding Value, Converter={StaticResource GroupByValueConverter}}"></TextBlock>                                  
                                </StackPanel>                           
                        </DataTemplate>
                        </ig:TemplateColumn.GroupByItemTemplate>
                    <ig:TemplateColumn.ItemTemplate>

  GroupValueConverter code

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {

            var view = (EntitySet<view1>)ViewModel;
                      return view.FirstOrDefault(row => row.ID== (int)value).Description;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }

        #endregion

        #region  object ViewModel (DependencyProperty)
        public object ViewModel
        {
            get { return (object)GetValue(ViewModelProperty); }
            set { SetValue(ViewModelProperty, value); }
        }
        public static readonly DependencyProperty ViewModelProperty =
            DependencyProperty.Register(
            "ViewModel",
            typeof(object),
            typeof(GroupByValueConverter),

        new PropertyMetadata(null, null));
        #endregion ViewModel (DependencyProperty)

Now it does not recognise the value

Any pointers what is missing?