Auto Resizing Problem

[Marcin]

I have following window:

<telerik:RadWindow x:Class="IdealHost.FaceToFace.Controls.MessageBox" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" MinHeight="140" MinWidth="300"
                   WindowStartupLocation="CenterOwner" ResizeMode="NoResize"  >

<Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="80" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <TextBlock VerticalAlignment="Center" HorizontalAlignment="Stretch" Grid.Row="0" Grid.Column="1" Margin="15,10,15,10" Name="txtMessage" />

          </Grid>
</telerik:RadWindow>

When I'm assigning text using following code:

this.txtMessage.Text = message;

The window is propery resized to size of text.

But when I change TexBlock to use Binding:

<TextBlock VerticalAlignment="Center" HorizontalAlignment="Left" Grid.Row="0" Grid.Column="1" Margin="15,10,15,10" Text="{Binding Message}"/>

The window is not automatically resizing. And text is cut.

How can I fix this issue? I realy would like to use binding not direct code.