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Fix: Api-ms-win-core-libraryloader-l1-1-1.dll Missing Error During Windows 10 Upgrade

When you try to upgrade to Windows 10 from a Windows 7 computer using the WIndows 10 Update Assistant tool, the following error may pop up:

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.

Precisely, the error message referencing the module api-ms-win-core-libraryloader-l1-1-1.dll occurs when upgrading from Windows 7 to Windows 10 Fall Creators Update v1709 using the update assistant utility from Microsoft. This error occurs because Microsoft seems to have packaged the wrong version of a DLL into the upgrader app. And the ultimate fix is to replace C:\Windows10Upgrade\wimgapi.dll with the one from C:\Windows\System32\wimgapi.dll.

  1. Open File Explorer and browse the Windows\System32 folder
  2. Find the wimgapi.dll file. Right-click and select copy.
  3. Browse the C:\Windows10upgrade folder
  4. Right-click on the folder background area, and click Paste.
  5. You’ll then be asked if you wish to replace the wimgapi.dll file with the new one. Select Yes.
  6. Close the folder(s) and re-launch the upgrade assistant.

The upgrade should now proceed smoothly!

See also: What is Windows10Upgrade folder and can I remove it?

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