Strange Behaviour in DataGrid SilverLight 3 Control - silverlight-3.0

Question

Here is the my Xaml Code. Here I have changed the Foreground of the cell depending on the current age of the person.
<data:DataGridTemplateColumn Header="First Name" Width="150" MinWidth="150" CanUserReorder="False" SortMemberPath="FirstName">
<data:DataGridTemplateColumn.CellTemplate>
<DataTemplate >
<TextBlock Foreground ="{Binding Path=DateOfBirth,Mode=OneWay,Converter={StaticResource CellColor}}" Text="{Binding FirstName}" ToolTipService.ToolTip="{Binding FirstName}" FontFamily="Arial" FontSize="11" VerticalAlignment="Center" Margin="5,0,0,0" />
</DataTemplate>
</data:DataGridTemplateColumn.CellTemplate>
</data:DataGridTemplateColumn>
<data:DataGridTextColumn Foreground ="{Binding Path=DateOfBirth,Mode=OneWay,Converter={StaticResource CellColor}}" Header="Last Name" Width="150" MinWidth="150" Binding="{Binding LastName}" CanUserSort="True" IsReadOnly="True" CanUserReorder="False"/>
When I run the above code it return following Exception
AG_E_PARSER_BAD_PROPERTY_VALU
My question is that when I remove the Foreground converter from the DataGridTextColumn Column it runs fine As the Foreground converter is applied in the DataGridTemplateColumn Column which will not through excepction. But when I used same Converter to the DataGridTextColumn it throw execption why, can anyone know why is th
is behaviour
thanks in advance.
Sorry Josh Einstein Here is the my return value from the converter
if (intAge > 25)
return new SolidColorBrush(Colors.Red);
else
return new SolidColorBrush(Colors.White);