How to Fix “Unknown structure” Build Error
After migrating or modifying Blueprint Structure assets in an Unreal Engine project it can happen that packaging the game would fail. Inside the output log you’ll find error messages pointing to ostensibly unknown Blueprint Structure assets. Next to the error you will also see the line “resave of source package /<GamePath>/<Structure Name> may fix issue.”. This gives us a good hint on how to fix the problem.
Solution 1 – Search for and resave assets manually:
- Find all problematic assets in the output log.
- Locate the assets in the content browser.
- Open and save each asset individually. To ensure the asset will be resaved properly, modify any containing value and change it back, then hit save.
- Package your game!
Solution 2 – Use the resave packages commandlet:
- Close the engine.
- Create a new text file and change the file extension from .txt to .bat.
- Open the file with a text editor and add following line:
C:\Program Files\Epic Games\UE_4.27\Engine\Binaries\Win64\UE4Editor.exe” “C:\<PATH TO PROJECT>\<PROJECT NAME.uproject>” -run=ResavePackages -fixupredirects -autocheckout -projectonly
- Change the command to match your directories and project name. The first path is pointing to your engine installation, don’t forget to update the engine version if necessary (for UE 5, it’s UnrealEditor.exe, not UE4Editor.exe). The second path in the command is the path to the project you want to resave packages in.
- Save and close the file, then double click it to run the command. (Yes, you could as well simply paste this into CMD, but this way the window doesn’t close right after execution. Besides, you might want to run this command again in the future.)
- Try packaging your game (this might not fix the problem in every case).