I have experimented with the same series of DVD Rips, using different bit rates, codecs, etc, and here is what I have discovered.
The new and improved 4.5 Media Player doesn't like MP4 files that have no audio track on them. I recalled that when I ripped these segments from DVD, I had disabled the audio because I only wanted the video portion of it.
I discovered this purely by accident, as I recently ripped a couple of DVD movies on to MP4 for use on my Curve. I then noticed that I did not have the trouble that I have previously described in this thread. That got me thinking a bit...
I was intrigued enough to go back to the original DVD and re-rip one of the files, both with sound, and then with no sound. The file with no sound hung the player as previously described. The file that had an audio track played perfectly.
So now I can continue to use my trusty Imtoo 3GP Converter (even though I use MP4), with no change, and since I have to re-rip those original files anyway, I'll now know to not disable the audio, and I can also use an even higher video bit rate.
Imtoo 3GP Converter (ImTOO DVD Ripper - DVD converter, Rip DVD to AVI, MP4, DivX, MPEG
My settings are the default BlackBerry MP4 settings but the default video bit rate is raised from 300 to 512. I leave the audio settings as they are.
Works like a charm!