How can I fix MSI error 2503 by adjusting folder permissions on Windows 10?

Permission issues are a primary cause. You need to ensure the `C:\Windows\Temp` folder has appropriate write permissions. Right-click on `C:\Windows\Temp`, select 'Properties', go to the 'Security' tab, and click 'Edit'. Add 'Everyone' (if not present) and grant 'Full control'. If 'Everyone' is not an option, ensure 'SYSTEM' and your user account have 'Full control'. Apply changes and try the installation again. You might also need to check permissions for the specific target installation directory if the error persists.