I capture MP4 videos with my phone and post them to YouTube.  When they require editing, I open them with Windows Movie Maker, edit them, save as MP4, and upload to YouTube.  I've done this successfully with hundreds of videos.

Lately I had two videos that wouldnt upload to YouTube.  I also tried opening them with Windows Media Player, and I get this error: "Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file."  One of the files I was able to open the Movie Maker project, edit it, re-save it, and it opened and uploaded with no problem.  The second file, which is a particularly long file (almost 100 minutes long) no mater what and how I save it, Media Player and YouTube wont open it.  I have had other long files work successfully.

Any suggestions?  Thanks!