I’m at a lost , why won’t it play, but will play quite nicely on my 5 year old computer?!?!
Because it’s a bad encode, but VLC has been written to (and advertises that it will) play bad/damaged files.
Whatever settings you used when you made the files that _ WILL _ work, go back and re-make the bad files with the same program and those settings – you know those settings are correct.