I just spend 3 hours trying to upgrade to Windows 10 on my lenovo X1 Carbon touch (2014 model).
The upgrade failed with error code 80240020 – Lots of suggestion on the net about deleting all content from the download folder in c:\windows\softwaredistribution. That didn’t work 🙁
The culprit turned out to be the driver for the builtin 4G LTE modem. From Sierra Wireless, the EM7345. This software have not been update by Lenovo System Update.