1) Open the Windows Device Manager.
Windows 7: Click on the Windows icon in the lower left, then select "Control Panel" -> "System and Security" -> "System" -> "Device Manager"
Windows 10: Right-click on the Windows icon in the lower left and select "Device Manager"
2) Expand the category "Network adapters". If you fthere is an entry labelled "TAP-Windows Adapter V9", uninstall it (including the drivers).
3) Reboot your system.
4) Now OkayFreedom should be able to repair itself.
If these steps do not solve the issue, the adapter installation might be blocked by your firewall, antivirus program or other installed VPN solutions. Please check if you can temporarily disable or remove those and then try again.