Fix Windows Defender Real Time Protection Error

1. Open registry editor (regedit)
2. Go to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
3. Create a DWORD (if not exists) with name DisableAntiSpyware
4. Set the value of DisableAntiSpyware to 0
5. Exit the registry editor and reboot

ref: http://www.thewindowsclub.com/error-0x80508020-0x800705b4-for-windows-defender