That error message is just a generic thing telling you that some function hasn't worked because some data do not exist.
The best thing is to make a backup of the project and then try to narrow things down. E.g try disabling 'clear folder' and then go through the overwrite boxes to see if you can export with one of those options disabled. Keep removing things* and trying to export until it works, then you can restore the backup and remove just that thing to confirm it.
*I don't just mean the checkboxes - if they're not the cause start removing things from the track.