I haven't checked your logs, as I am not an expert, but I had a similar problem so you can try my solution if you want.
Close MediaPortal and open MediaPortal Configuration
Go to "DVD Post Processing"
In the list of "Available Filters" find "ffdshow Video Decoder" and double click on it (it will then show up in the "Activated Filters" list above.
Highlight "ffdshow Video Decoder" in the "Activated Filters" list and then click "Filter Properties" which will open up the filter properties window for the processor.
In the new window, select "Codecs" on the left hand side and then navigate to "MPEG2" in the table of codecs, Highlight "MPEG2" and at the bottom of the properties window there is a tick box to enable "DVD Decoding" which you need to put a tick in.
Then, next to MPEG (which is in the "Format" column in the table), Click in the "Decoder" column which will give a drop down box. Select "Libmpeg2" from the list.
Click OK.
Now find "ffdshow Audio Decoder" in the "Available Filters" list double click on it (but you shouldn't need to change any options unless you are up/down mixing the sound for your specific system requirements).
Click OK to close MediaPortal Configuration and run MediaPortal.
Now try a DVD.
Please feed back if this works as I find that lots of people don't say if fixes work so others don't know if they should try the solution or not in the future.
Robbo100