Children.Add(item) value does not fall within the expected range

I'm developing a Silverlight 3 app and getting this really weird error when I try to add an object to a Canvas. My code is as follows: ``` for (int i = 0; i < person.Children.Count; i++) { //Add children in same position as parent Person child = person.Children[i]; child.x_PositionTransform.X = person.x_PositionTransform.X; child.x_PositionTransform.Y = person.x_PositionTransform.Y; child.Click += new RoutedEventHandler(person_Click); x_LayoutRoot.Children.Add(child); } ``` The first time I use this, it works as expected. However, when I hit x_LayoutRoot.Children.Add(child) after clicking a Person object that was created using this code, I get an ArgumentException telling me that "Value does not fall within the expected range." However, when I add the following code before adding child to x_LayoutRoot.Children, the problem disappears. ``` child.SetValue(Canvas.NameProperty, "child" + objCount++); ``` Why is this happening? Is this a Silverlight bug, or (more likely) am I just missing something?