Make sure you upload all the 6.4.2 files and if you upgraded from 6.4, make sure you ran the 6.4-6.4.1 altertable.
Don't trust the changedfiles list.
If the version number didn't change after upgrade - it means you either didn't upload all the files or you didn't edit the config file after upgrade. Try uploading all the files and then edit the config file.