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Unreal Engine Troubleshooting

Fixing Plugin Cook Errors and Additional Directory Warnings

When packaging an Unreal Engine project, developers often encounter 'unknown cook error' or runtime warnings stating a plugin must be included as an additional directory. This typically occurs when assets within a plugin, such as UI Navigation 3.0, are not explicitly registered in the project's packaging settings, leading to broken title screens or failed builds.

Published March 13, 2026 5 min read Unreal Engine

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1. The Duplicate Asset Trap

A common reaction to 'missing directory' warnings is to manually copy the plugin folder from the Engine's Marketplace directory into the local project's Content folder. This is a critical mistake that leads to an 'unknown cook error'.

By duplicating the plugin files, you introduce naming collisions. The Unreal Editor sees two versions of every asset—one in the engine folder and one in your project—and fails the cook process because it cannot resolve the duplicates.

  • Avoid moving plugin files into the local /Content/ directory manually.
  • Watch for logs flagging duplicate items during the cook phase.
  • Check if the plugin is already globally installed in the Engine's Marketplace folder.

2. Configuring Additional Asset Directories

The definitive solution lies in the Project Settings, specifically under the Packaging section. Rather than moving files, you must inform the cooker where to find the plugin's internal assets using relative paths.

In the 'Additional Asset Directories to Cook' array, you should not point to the Windows file system path. Instead, use the internal Unreal path format that targets the specific subfolders within the plugin.

  • Open Project Settings > Packaging.
  • Locate 'Additional Asset Directories to Cook'.
  • Add an entry using the format /PluginName/SubFolderName (e.g., /UINavigation/Input).
  • Ensure the same is applied to 'Additional Non-Asset Directories to Copy' if the plugin contains raw data.

3. How to Verify the Fix

Once the paths are correctly mapped, delete the 'Intermediate' and 'Saved' folders in your project directory to clear any cached cook data that might still reference the old, duplicate files.

Relaunch the editor and attempt a clean package. If the 'unknown cook error' persists, check the Output Log for the specific string 'LogCook: Error'. If the path configuration is correct, the log will no longer report missing directories on the title screen.

Key snippets

Packaging Setting Path Format

plaintext

Use this relative path format in 'Additional Asset Directories to Cook' to resolve plugin asset warnings.

/UINavigation/Input

FAQ

Why can't I select plugin folders via the file browser in Project Settings?

The file browser often defaults to the project's internal Content folder. To include a plugin, you must manually type the internal path starting with the plugin's name (e.g., /PluginName/Folder) rather than selecting a folder on your hard drive.

Does this require a C++ project?

No, this specific configuration for asset directories is handled via the Project Settings UI and applies to both Blueprint-only and C++ projects.

References

  • UI Navigation 3.0 External Reference

    Mentioned in the first post.

    https://www.fab.com/listings/a91f6e67-5c2d-46ef-926d-00a35525579c

  • image 1923×130 5.86 KB Community

    Mentioned in the high-value reply.

    https://forums.unrealengine.com/uploads/short-url/pTEqaUtSpnrgqutaF9XWLJN956L.png?dl=1