My Prolific USB-to-Serial converter has been working well on Windows XP but refuses to work on Windows 7 64-bit. Windows first complained that the driver is unsigned:
and after that complained that the driver cannot be installed:
The root cause is clear – the Prolific USB-to-Serial driver is not compatible with Windows 7 because it is unsigned. Despite me choosing to install the driver anyway, Windows still refused to install it. After half a day trying various suggestions, I finally came up with a solution
1. Go to the registry branch HKLMSOFTWAREPoliciesMicrosoftWindows NTDriver SigningBehaviorOnFailedVerify and set value as DWORD 0. This prevents Windows from rejecting unsigned drivers.
2. Open a command prompt and perform the following commands to enable Windows Test Mode, make use to use “Run as administrator”:
- bcdedit.exe -set loadoptions DISABLE_INTEGRITY_CHECKS
- bcdedit.exe -set TESTSIGNING ON
3. Use this tool to sign the driver and allow it to be used when Windows is in test mode. This applies to all DLL and SYS files in the driver package.
4. Reboot your machine and Windows should report that it is running in Test Mode at the bottom right corner:
5. Proceed to install the driver as per normal. Windows should accept the driver and install successfully:
The Prolific USB-to-serial driver can also be downloaded here, in case you’re looking for it.