The code above works fine (without exception) with the latest version 4.7, however, still there is problem in embedded images conversion from msg to rtf. Only text is currently converted. It's a known issue and we are working on it.
The issues you have found earlier (filed as 7774) have been fixed in [this update ](http://www.aspose.com/community/files/51/.net-components/aspose.network-for-.net/entry220477.aspx).