Wpf calendar combobox multibinding

See more:

WPF

C#4.0

Hello,
i hava got a WPF, C# problem. I want to get the combobox value into the calendar

The WPF Code:

  <ComboBox Name="cbWorker" HorizontalAlignment="Left" Margin="96,10,0,0" VerticalAlignment="Top" Width="198"
   ItemsSource="{Binding Path=Companies}" SelectedItem="{Binding Path=Company}"  >
                  </ComboBox>

 <Label Content="{Binding Path=Company}" HorizontalAlignment="Left" Margin="10,6,0,0" VerticalAlignment="Top"/>

<Calendar Name="Kalender" Tag="{Binding Path=Company}" SelectedDatesChanged="Calendar_SelectedDatesChanged" HorizontalAlignment="Left" Margin="10,10,10,10" VerticalAlignment="Top">
                <Calendar.CalendarDayButtonStyle>
                    <Style TargetType="{x:Type CalendarDayButton}">
                        <Setter Property="Background" >
                            <Setter.Value>
                                <MultiBinding Converter="{StaticResource formatterView}">
                                    <Binding Path="Company" />
                                    <Binding Path="Date" />
                                </MultiBinding>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </Calendar.CalendarDayButtonStyle>
            </Calendar>

The problem is that the Label shows the right value but the multi binding says {DependencyProperty.UnsetValue} for the ComboBox value.

What I have tried:

The label to show the value but it works and only the multi Binding did not work.