Complete newb with C#

Code:

private void ProductName_TextChanged(object sender, TextChangedEventArgs e)
{
    lblCharactersLeft.Content = (ProductName.MaxLength - ProductName.Text.Length).ToString();
}

Try this. Apparently in XAML, labels use .Content instead of .Text, and the event is TextChangedEventArgs e instead of a generic EventArgs e.

What compiler/editor are you using, Fiel?