I think I've found the problem, or that or coincidence, but I noticed that among the files that had not been uploaded any had the character ' in the name, I also saw that when the client then tried to download that file, he did so a weird character instead. Therefore I have removed that character from the name of the files and I have uploaded it again and this time it uploaded correctly. I hope that someone with this problem will read this and can solve his problem in this way.
That is/was exactly your problem. FYI, so give your future torrent names a good glance over for unusual characters in the type. Glad you got it addressed. 🙂