Windows Update error (Your device is missing important security and quality fixes)

I had this problem for a long time and tried many different methods. The problem is that Windows Update, when it fails, does not provide enough error information. I found out that if one uses the online Windows Update (https://www.microsoft.com/en-us/software-download/windows10, then choose Update now), it may give you additional information about why the update failed. In my case, it said "You can't install Windows on a USB flash Drive using setup". A little search revealed that it was caused by HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\PortableOperatingSystem was set to 1. After changing it to 0, I went through the online update successfully. Hope this helps.