For purposes of sharing, here is what I did to finally successfully Install

the Prolific Driver on my W8.1 64bit machine. The solution was getting

the correct "SER2PL64.SYS" file. Thanks to those here, a Microsoft

MVP, and Prolific for their patient assistance.

On my windows8 64b computer I started by installing the windows 8 driver

PL2303_Prolific_DriverInstaller_v1.11.0.zip  It's on the

http://www.prolific.com.tw/US/CustomerLogin.aspx website (use guest/guest

for user and password).

(This direct prolific driver download link might work too)

IMPORTANT: My past problem was missing the right .SYS file in

c:\windows\system32\drivers folder. Get the correct ser2pl64.sys file here:

(this file, only 64000 bytes compaired to the original that was over 150K)

Next I ran the Prolific_DriverInstaller_v1.11.0.exe (from the above zip). Next

I copied the 64K ser2pl64.sys file into the Windows8 C:\Windows\System32\Drivers

folder (overwrite the original although it may be prudent to first rename

the original to ser2pl64.OLD)

Then I plugged in my usb to serial cable, if the cable is not correctly recognized,

remove the cable. Now right click the Prolific driver listed under the "Ports

(Com&LPT)" listing in Device Manager and click "upgrade the driver"; next

highlight "search the local machine" and pick Prolific_3_2_0_0 from the

list. Re insert the USB cable.

After many frustrating attempts, this finally worked for me.

Mike K5HUM