You must follow ever step in the process in exact order.
If you still receive an error after running the
PL-2303_64bit_Installer.exe and your device is plugged in - go to
Windows Device Manager.
Windows Vista/7/8/10: Control Panel » System » Device Manager
Windows XP: Control Panel » System » "Hardware" tab » Device Manager
Scroll down to Ports (Com & LPT) and double-click on "Prolific
USB-to-Serial Comm Port (COM#)".
In the Properties Window, Click on "Driver".
The "Driver Version" must say "22.214.171.124" dated 09/24/08.
If not, then the correct driver is not installed.
Unplug the USB-To-Serial adapter and run the
"PL2303_64bit_Installer.exe" again - following the directions precisely
until the correct driver appears.