When using an external DVD player application the Cannot play DVD always appears when returning to MP. This occurs with Autoplay DVD enabled and disabled

To reproduce:
- Setup an external app for DVD playing
- Open MP
- Goto My Video
- Press Play DVD (the external app starts)
- Close the extrnal application
- The "Cannot play DVD" dialog will now be displayed

Original thread: http://nolanparty.com/mediaportal.sourceforge.net/phpBB2/viewtopic.php?t=1467