Silverlight Image binding Issue

I am trying to bind web address of an image (BigImageURL) with a image control. It works fine mostly but for some images i am getting http 403 error (found out using fiddler) and obviously the image does not get displayed. I want to display a static image in case the http url is not resolved.

<Image x:Name="HoverImage" Source="{Binding BigIma开发者_Python百科geURL}" />

I tried to write a converter

public class UriToImageSourceConverter : IValueConverter
{

    public object Convert(object value, Type targetType,object parameter, CultureInfo culture)
    {
        BitmapImage image = null;
        try
        {
             image = new BitmapImage(new Uri(value.ToString()));
        }
        catch (Exception ex)
        {
            image= new BitmapImage(new Uri("..<mydefaultimageUrl>.."));
        }
        return image;
    }

    ...
}

<Image x:Name="HoverImage" Source="{Binding BigImageURL,Converter={StaticResource myUriToImageSourceConverter}" />

didn't work !! Even though the image url was not accessible, the converter didn't throw any exception. I don't think it tries to resolve the address or read image stream while creating the BitmapImage

Tried setting up a FallbackValue but it didn't work either.

 <Image x:Name="HoverImage" Source="{Binding BigImageURL,FallbackValue=DefaultUrl}"/>

Any pointers ??

Thanks in advance

Actually you have to do something like this

 <Image x:Name="HoverImage" Source="{Binding BigImageURL}" 
        ImageFailed="HoverImage_ImageFailed" />

and add event handler

    private void HoverImage_ImageFailed(object sender, ExceptionRoutedEventArgs e)
    {
        var expection = e.ErrorException; // Here we could know what happend
        HoverImage.Source = someDefaultUrl; // And here we add default Url...
    }

In silverligth you have to handle not loader image and image exceptions with help of events... do not use databinding for that case..