A digitally signed driver is required
When installing old drivers on a new operating system there is a possibility that they have not be signed with the appropriate certificate. Since Windows Vista this is a requirment for all drivers on a 64 bit operating system.
There are 2 solutions of how to bypass this error. One for Windows 7 and one for Windows 8 / 8.1:
1. Restart your computer and press F8 to go into the Advanced Boot Options:
2. Select the “Disable Driver Signature Enforcement” option to bypass the Driver Signature check. Once booted in Windows you should be able to install the Driver
Windows 8 / 8.1
1. Press Win + C and click on Settings
2. On the Settings tab press “Change PC Settings”
3. In the Control Panel screen press “Update & recovery”
4. Followed by “Recovery – Advanced Startup – Restart now”
5. Once rebooted in the Advanced startup mode select “Troubleshoot”
6. Select “Advanced options” in the Troubleshoot screen
7. Followed by “Startup Settings”
8. We’d need to reboot one more time to modify the boot configuration settings:
9. Once rebooted in the Startup Settings press “F7” to Disable driver signature enforcement
Your computer will reboot and once booted up in Windows you’ll be able to install the conflicting driver.
As you can see things have become a little more complicated in Windows 8 / 8.1 compared to Windows 7.