I'm sorry for the frustration. I've seen the Update Error 18 in two cases.

1) A file was really, really corrupt. I couldn't rename it, I couldn't move it, I couldn't delete it.  

2) With Avast AntiVirus installed - it's RansomeWare protection feature blocks our direction.  Do you have anything like that which could be interfering?  If so, I'd double check it and see if it has any of our directories or executables under watch or in quarantine.

Either way, the following worked

- Backing up any data files, just in case (i'd just copy in File Explorer the entire data directory)

- Rename [installation directory]\32bit to 32bit_backup

- Run the installer again