Copy the following image from the browser and paste it to RadRichTextEditor: https://en.wikipedia.org/wiki/File:Telerik_Logo.png. IOException is thrown when pasting the image. However, it is loaded at the end.

Export the image with the following code:

private void radButton1_Click(object sender, EventArgs e)
{
    DocumentFormatProviderBase provider = new XamlFormatProvider();
    byte[] byteData = provider.Export(this.radRichTextEditor1.Document);
}

ArgumentException occurs. 

Workaround: save the image first and copy it from Paint for example.