Ok. What is the DVD navigator? BTW - I'm a .NET C# developer and a former MythTv user and I'm so far very impressed with this. If I can get DVD and HDTV working, I'm definitely donating. Kudos!
If you download graphedit (google for it), and select 'insert filter' from the menu, you'll see list of directshow filters. 'DVD Navigator' is one of these. Insert it. It has three pins. Right click on these select 'render pin'. One of these will most likely result in the same error you're seeing in your logs.
Try it and you'll see what I'm on about.
Its something to do with the combination of directshow filters installed on your machine.