I think that Leawo has helped me to solve the problem. The MP4 files that I made using the old version of Blu-Ray Ripper apparently defaulted to H.264 video codec for MP4 files. Twonky is able to read those files.
The new version (7.3.0.3) of Leawo Blu-Ray Ripper defaulted to MPEG4 video codec. Twonkey cannot read those MP4 files. I have changed the video codec to H.264 in Blu-Ray Ripper and I am in the process of ripping a DVD now. I will post the result.
