Microsoft responded to a report of the 0xC1900101-0x30018 installation error with a requirement that all antivirus programs be uninstalled, then re-installed, once the upgrade was complete. This may have had an effect, but there are many other "3rd party" apps that may have caused this error. The recommendation is to just re-install your former Windows package, and call Microsoft to re-use your product key, and THEN the Windows 10 Upgrade will work, and THEN you can re-install Norton AntiVirus... Just sayin'...