What i do wrong here

 <ig:XamDialogWindow x:Name="popSelectUsage" WindowState="Hidden" IsModal="True" StartupPosition="Center" HeaderIconVisibility="Collapsed" MinimizeButtonVisibility="Collapsed" Width="850" VerticalContentAlignment="Stretch">
                <controlsToolkit:BusyIndicator  x:Name="busySelectUsage">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*"></ColumnDefinition>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                        </Grid.RowDefinitions>
                        <StackPanel Grid.Row="0">
                            <data:DataGrid x:Name="gridAsmtList" Grid.Row="2" AutoGenerateColumns="False" HorizontalAlignment="Center"  Margin="5,5,5,5" GridLinesVisibility="None">
                                <data:DataGrid.Columns>
                                    <data:DataGridTextColumn Binding="{Binding Name}" Header="Name"></data:DataGridTextColumn>
                                    <data:DataGridTextColumn Binding="{Binding SuggestedUnit}" Header="Unit"></data:DataGridTextColumn>
                                    <data:DataGridTextColumn Binding="{Binding SuggestedQuantity}" Header="Quantity"></data:DataGridTextColumn>
                                    <data:DataGridTextColumn Binding="{Binding SuggestedUsage}" Header="Used"></data:DataGridTextColumn>
                                </data:DataGrid.Columns>
                            </data:DataGrid>
                        </StackPanel>
                    </Grid>
                </controlsToolkit:BusyIndicator>               
            </ig:XamDialogWindow>

When the XamDialogWindow popup the Height of the popup doe snot expand base on the height of the Datagrid