I had a similar problem. Turned out to be a problem with the FTP client, as it seems. I had used FileZilla under Linux and got this problem, even after several uploads (all without any errors reported from FileZilla). I also tried uploading the ZIP and then extracting it with a web-based filemanager provided by the hoster.
Then I uploaded the extracted files of 2.3.3 with Krusader. And suddenly, the setup worked without any problems.
There have been many reports of corrupted or missing files when transferring them individually with FTP. See the method here for an alternative:
http://bobsguides.com/modx-upgrade-faq.html