Error code 0x80240020 occurs if the session ID of the running Windows 10 setup is invalid.
This may occur if the user logged off Windows while setup was still running.
In order to resolve this issue you need to rename the following folders, and then check for updates again.
Note that the second folder is hidden.
In order to avoid this error do not log off Windows when the Windows 10 Setup is still running.
UK based technology professional, with an interest in computer security and telecoms.