# UEFN fails to launch — "Failed to open descriptor file" + ICU crash (Release 41.20) 

**URL:** <https://forums.unrealengine.com/t/uefn-fails-to-launch-failed-to-open-descriptor-file-icu-crash-release-41-20/2736835>\
**Category:** Issues and Bug Reporting\
**Tags:** unreal-engine, unreal-editor-for-fortnite, crash, bug-report, editor\
**Created:** [July 19, 2026, 1:05pm UTC](https://forums.unrealengine.com/t/uefn-fails-to-launch-failed-to-open-descriptor-file-icu-crash-release-41-20/2736835 "2026-07-19T13:05:26Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Wuoli19](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Wuoli19](https://forums.unrealengine.com/u/Wuoli19)\
**Post date:** [July 19, 2026, 1:05pm UTC](https://forums.unrealengine.com/t/uefn-fails-to-launch-failed-to-open-descriptor-file-icu-crash-release-41-20/2736835/1 "2026-07-19T13:05:26Z")

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### Summary

UEFN crashes on launch and never opens, on Fortnite/UEFN build ++Fortnite+Release-41.20 (Windows 11).

On launching UEFN from the Epic Games Launcher, a “Corrupt/missing files detected” dialog appears. Choosing either option then shows:

“Failed to open descriptor file ../../../FortniteGame/FortniteGame.uproject”

followed by a fatal error:

“ICU data directory was not discovered: ../../../FortniteGame/Content/Internationalization”

The editor never opens. Fortnite and Save the World both launch and play fine on their own, and both are installed on the same drive as UEFN. UEFN self-aborts on the descriptor/ICU check rather than crashing a module, which points to the UEVFS virtual file system failing to mount Fortnite content — likely a build-side regression, as other users report similar crashes on 41.20.

LoginId: c2516a414951ffd466dea3adecf4cd5c

### Please select what you are reporting on:

Unreal Editor for Fortnite

### What Type of Bug are you experiencing?

Other

### Steps to Reproduce

1. Install Fortnite and UEFN via the Epic Games Launcher (both on the same drive)
2. Launch UEFN from the launcher’s “Launch” button
3. A “Corrupt/missing files detected” dialog appears; choosing either option leads to the crash

### Expected Result

UEFN opens normally and the editor loads.

### Observed Result

UEFN crashes before the editor opens. First a dialog shows:  
“Failed to open descriptor file ../../../FortniteGame/FortniteGame.uproject”  
Then a fatal error:  
“ICU data directory was not discovered: ../../../FortniteGame/Content/Internationalization”

LoginId: c2516a414951ffd466dea3adecf4cd5c

Already tried without success: verified both Fortnite and UEFN multiple times, clean reinstall of UEFN, cleared %localappdata% caches (FortniteGame, UnrealEditorFortnite) + reboot, ran launcher as administrator, confirmed user path has no special characters, toggled off Windows Sandbox/virtualization. Fortnite and Save the World both launch fine on their own. Version ++Fortnite+Release-41.20.

Event Viewer shows no application module fault — UEFN self-aborts on the descriptor/ICU check, which suggests the UEVFS virtual file system isn’t mounting Fortnite content. Appears to be a build-side regression; other users report similar issues on 41.20.

### Platform(s)

Windows 11 (PC)

### Upload an image

 ![Captura de pantalla 2026-07-19 035456.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/9/7/d/97de0358f71a2dd3c0f7e2976383fcb27ef085a9.png) ![Captura de pantalla 2026-07-19 035443.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/8/5/6/8560f09a38df3f3101efe6fe2c5b87816f5272a4.png)

### Additional Notes

Event Viewer shows no Application Error module fault for UEFN — it self-aborts on the descriptor/ICU check rather than crashing a module. This points to the virtual file system (UEVFS) failing to mount Fortnite content, which looks like a build-side regression rather than a local configuration issue. At least one other user reported an identical crash on a recent build.

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<div class="post-metadata">

**Author:** ![Jimbohalo10](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/jimbohalo10/32/961440_2.png) [@Jimbohalo10](https://forums.unrealengine.com/u/Jimbohalo10)\
**Post date:** [July 19, 2026, 6:59pm UTC](https://forums.unrealengine.com/t/uefn-fails-to-launch-failed-to-open-descriptor-file-icu-crash-release-41-20/2736835/2 "2026-07-19T18:59:21Z")

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hi @Wuoli19

Please run verify on your installation.

[How to Verify Fortnite/UEFN](https://forums.unrealengine.com/t/urc-exe-and-urc-dll-get-flagged-as-malware-from-microsoft-defender/1802519/5)

If this still fails you might have to uninstall Fortnite/UEFN and reinstall as looks like some parts did not get installed correctly in the patch update