Cannot open MP4s to change tag data

I have several thousand MP4 video files of segments of lectures, perhaps 100 different lectures. I am trying to edit the tag information to add disc number and track number. Of the 2,500 different MP4s, 99% worked. But about 35 did not work. The MP3Tag app said they could not be opened. They were randomly dispersed across the various courses, so I am not sure what is wrong with them, nor how to fix the problem. The videos seem to work fine, I just can’t edit the tag data.

Does anyone have any suggestions?

I found this thread: