I ran into an issue trying to upgrade a Windows 7 machine to Windows 10. I kept getting an error that said…

Windows10UpgraderApp.exe - System Error

The program can’t start because api-ms-win-core-libraryloader-l1-1-1.dll is missing from your computer. Try reinstalling the program to fix this problem.

I read through this article and found the solution and I wanted to re-post it for my future use.

  1. Close the Windows 10 updater app, if open.

  2. Copy the file at C:\Windows\System32\wimgapi.dll

  3. Replace the file at C:\Windows10Upgrade\wimgapi.dll

That’s it! You should be able to upgrade to Windows 10 without any other DLL issues.