Not without a lot more detail from you. Specifically about your computer, operating system, hardware, version and variant of MEP you are running, etc., etc..
Also it would be very helpful to see what the Text view in the free MediaInfo utility says about one of the files that will not play or upload. Remember, .mp4 is a "container" format; the actual codecs used to create the file and also needed to play it back, can vary enormously!
Here we go Windows 10 Pro, 64 bit operating system, its MEP 2016, its been running fine after rendering then wont play on the built in media player on the PC, it does however play on VLC, but the file wont upload to Vimeo... I was wondering if it could be something to do with he MP4 setting in MEP.. or th media player i use... I bought the codec for MP4 on the update/installation , but again been running fine until today...
But the MediaInfo data is the really crucial part that is missing. If you don't already have this very useful, free utility, you can download it from here. Simply install it and point it to one of your files which you cannot play or upload to Vimeo; post the results here, as I asked in my previous post.
I don't personally use Vimeo so can you also post details of that site's format and media requirements for mp4 videos?