RichTextBox throws exception when dragging and dropping inside it

Question

I have a RichTextBox and when I try to drag & drop inside it it throws exception:

it happens when I'm in debug mode and the common language runtime exception flag is on.

This is my XAML -

<Grid>
    <RichTextBox x:Name="rtb"
                 ScrollViewer.VerticalScrollBarVisibility="Auto"
                 IsReadOnly="True" />
</Grid>

this is code behind -

public MainWindow()
{
  InitializeComponent();
  rtb.AppendText("aaaaaaa aaaaaaaaaaa aaaaaaaa aaaaaaaabbb bbbbb bbbbb bbbb");
}

Answer 1

Have you set AllowDrop = true ?
If you haven't, you can get bizarre errors