I had the same problem. Even after closing ProScan. It still wouldn't download. So, I had to go directly to the website and, download the update from there .You'll have to go to the ProScan web site and download it from there and install it. I ran into the same problem and that's what I had to do. There is some sort of problem with the auto update.
Please note: To install ver. 16.2, visit the ProScan web site then download and install. Exit ProScan before installing. This is due to previous ProScan versions using SSL TLS 1.1 and not TLS 1.2 and combined with my host removing TLS 1.1. So previous versions will not download the latest version within ProScan.