Windows 10 Upgrade Error: Windows Might be Installed in Unsupported Directory

When trying to upgrade the current Windows 10 build to 1809 (October 2018 Update) using the ISO file, I have come across an interesting problem. At the stage of selecting system settings to be saved during the upgrade, the option of keeping personal files and apps was inactive, and the wizard offered only one upgrade option when all personal user data and apps were going to be deleted (Nothing option). Meanwhile the following message was displayed at the bottom:

At first it seemed to me that I wouldn’t be able to upgrade the Windows 10 build from 1803 to 1809 and keep all user data, and I would have to reinstall the Windows in a clean install mode. However, the problem was only in the fact that the upgrade wizard could not find default Windows 10 app folders (getting ahead, I’d say that in my case they were specified incorrectly on some reason).

You can fix the problem by editing the registry. To do it:

1. Run the Registry Editor – regedit.exe;
2. Go to the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion;
3. Find the registry parameter named ProgramFilesDir. It must contain the full path to the directory where the system ‘Program Files’ folder is kept. If your system is installed on drive C:, the value of this parameter must be C:\Program Files. If the system is installed on another drive, the path will be different, for example, E:\Program Files;
4. Edit the value of this parameter so that it contains the full path to Program Files directory in your Windows 10 installation;
5. In the same way, check the values of the following parameters: ProgramFilesDir(x86), ProgramFilesPath and ProgramW6432Dir. If Windows 10 is installed on the C: drive, the following paths should be listed there:ProgramFilesDir(x86) = C:\Program Files (x86)
ProgramFilesPath = C:\Program Files
ProgramW6432Dir = C:\Program Files
   Tip. Instead of paths, you can use Windows environment variables. For example, you can use %ProgramFiles(x86)% variable as the value of ProgramFilesDir(x86) parameter, and %ProgramFiles% for the ProgramFilesPath.
6. Close the Registry Editor, restart your computer and start Windows 10 upgrade wizard again.

Please, also make sure that you haven’t redirected standard Windows app folders or the user profile directory (C:\Users\) to another drive using symbolic links. It can also cause this problem.