vertical scrollbar not appearing in datagrid inside usercontrol in wpf

UPDATED: I just took DataGrid out of StackPanel. Try this code:

<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="45.361"></RowDefinition>
    <RowDefinition Height="102.639" />
    <RowDefinition Height="30"></RowDefinition>
  </Grid.RowDefinitions>
  <Grid.ColumnDefinitions>
    <ColumnDefinition Width="2*"></ColumnDefinition>
    <ColumnDefinition Width="*"></ColumnDefinition>
  </Grid.ColumnDefinitions>

  <StackPanel Grid.Row="0"
              Grid.Column="0"
              Orientation="Vertical">
    <StackPanel Orientation="Horizontal">
      <Button>Add</Button>
      <Button>Remove</Button>
      <Button>Refresh</Button>
    </StackPanel>

    <Label Name="lblTopMessage">some message</Label>

  </StackPanel>

  <DataGrid Grid.Row="1"
            Name="dg"
            IsReadOnly="True">
    <DataGrid.Columns>
      <DataGridTextColumn Binding="{Binding Name}"
                          Header="Name"
                          Width="*"></DataGridTextColumn>
      <DataGridTextColumn Binding="{Binding Value}"
                          Header="Value"
                          Width="130"></DataGridTextColumn>
      <DataGridTextColumn Binding="{Binding List}"
                          Header="List"
                          Width="*"></DataGridTextColumn>
    </DataGrid.Columns>
  </DataGrid>

  <Grid Grid.Row="0"
        Grid.Column="1"
        Name="gridTS"
        Grid.RowSpan="2">
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="Auto"></RowDefinition>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="100"></ColumnDefinition>
      <ColumnDefinition Width="*"></ColumnDefinition>
    </Grid.ColumnDefinitions>
    <TextBlock Name="lblNewSource"
               Grid.Row="0"
               Grid.ColumnSpan="2"
               HorizontalAlignment="Center"
               Padding="0 5 0 0"
               FontWeight="Bold">New Source</TextBlock>
    <TextBlock Grid.Row="1"
               Grid.Column="0"
               Padding="10 10 0 0">Name:</TextBlock>
    <TextBlock Grid.Row="2"
               Grid.Column="0"
               Padding="10 10 0 0">Value:</TextBlock>
    <TextBlock Grid.Row="3"
               Grid.Column="0"
               Padding="10 10 0 0">List:</TextBlock>

    <TextBox Grid.Row="1"
             Grid.Column="1"
             Name="txtName"
             IsEnabled="False"></TextBox>
    <ComboBox Grid.Row="2"
              Grid.Column="1"
              Name="cbValue"></ComboBox>
    <ListBox Grid.Row="3"
             Grid.Column="1"
             Name="lbList">
      <ListBox.ItemTemplate>
        <DataTemplate>
          <CheckBox Margin="3 5 0 3"
                    Content="{Binding Name}"
                    IsChecked="{Binding IsActive}" />
        </DataTemplate>
      </ListBox.ItemTemplate>
    </ListBox>

    <Button Name="btnSave"
            Grid.Row="4"
            Grid.Column="1">Save</Button>
    <TextBlock TextWrapping="WrapWithOverflow"
               Name="lblMessage"
               Grid.Row="5"
               Grid.Column="1"
               Margin="0 10 10 0"></TextBlock>
  </Grid>
</Grid>

I hope that helps.

Make the vertical scrollbar appear and still keep the height of DataGrid auto.
The answer is NO.

As long as the height is auto it will grow as auto means I get all the height I want.

<RowDefinition Height="Auto"></RowDefinition>

If you want it to use available space then use *

<RowDefinition Height="*"></RowDefinition>