h.264 video freezing at 40:30;xx

I've run into this problem with several productions, each using different files. Using Handbrake, I've ripped DVDs to MP4s (H.264 codec). Several of the DVDs yield multiple MP4s, so I drop them into PPro to export a single .mp4. However, the video freezes around the 40:30 mark (productions are all over 60 min in length), audio continues to play. Any clues on cause, or workarounds? Different codecs (MPEG-4, Sorensen 3 & others) produce a file that plays fine, but size is too large for my purposes. (I'm looking for files in the 2Gb or less range for web download.)

Mac OSX 10.5.8
Using standard H.264 preset in Adobe Media Encoder (NTSC DV High Quality)
PPro 4.2.1
AME 4.2.0.0006

Craig