Upgrade Windows 7 to Windows 10 via MDT: The system registry cointains invalid file paths
Solution 1:
This exact problem is discussed in the post Issue when updateing from windows 7 pro to windows 10 pro.
Three workarounds were mentioned which worked for some (but not for everyone), as follows.
1. Incorrect PATH
One poster deleted everything in Path under System Variables except the following:
%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\
Check if you have any unnecessary item in the PATH in addition to the above entries.
2. Assigning drive letter 'A' to the "System Reserved" partition
This was done using Disk Management. It seems like a weird solution, but it was reported as working by one guy.
3. Tweaking.com windows repair
The poster downloaded and ran Tweaking.com - Windows Repair Portable and reports:
I can't remember which items exactly I ticked but pretty much resetting all the services, Windows update, firewall etc. Then rebooted and tried the Win10 1909 upgrade, and it worked perfectly.