[CRITICAL] Unable to launch session – “At least 1 module failed remote validation”

[supreeeeemeeeee (SupremeUEFN)]

Summary

This issue is happening on one of my projects where I am unable to launch a session. Whenever I try, it fails with the error: “At least 1 module failed remote validation.”

I haven’t been able to identify what is causing this. It’s also not limited to just me, multiple people in the community and on my team are experiencing the same problem.

Previously, switching accounts would temporarily allow the session to launch, but now both of my accounts are affected and returning the same error.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Other

Steps to Reproduce

Attempt to launch a session on the affected project. (This may not occur on other projects, as only this one is impacted.)

Expected Result

The session should launch successfully.

Observed Result

Launching the session fails with the error “At least 1 module failed remote validation” preventing the session from starting.

Platform(s)

PC

Upload an image

Additional Notes

We really hope this gets resolved soon, as it’s heavily impacting our work. We will be unable to update existing maps or launch new ones if this error occurs across all team members accounts.

Here are some related threads:

500×500 2.84 KB

Summary When i try to launch a session on my main account, I get “At least 1 module failed remote validation” error, but launching a session on the same project from a different account works fine (Same PC). and that goes for every single project. i created this new project to confirm it’s not project-related. Project ID: 75fb80f8-47e1-5de1-7ef2-2aa8abc939d8. Please select what you are reporting on: Unreal Editor for Fortnite What Type of Bug are you experiencing? Other Steps to Reproduce Ope…

500×500 2.84 KB

Hi, I had the same issue and found a solution. The problem is related to the team and your account. If you can leave the team and return, the issue will be resolved. Another option to resolve the issue would probably be to transfer the project to another team.

[Bug-Reporter]

The status of FORT-1039603 changed to ‘Needs Triage’. We’ve confirmed the issue and it’s waiting to be assigned to someone to fix it.

[HeyPickledDave (Dave)]

@supreeeeemeeeee please try this and let us know if it fixes your issue?

[supreeeeemeeeee (SupremeUEFN)]

Hey Dave, This isn’t available in my UEFN (5.8.0-49564179+++Fortnite+Release-39.20)

[HeyPickledDave (Dave)]

that’s unfortunate
I’ve made a request to clear your account’s cache.
I’m going to DM you the account id I fetched from the log I had, but you said you had two accounts that were broken so it’d be good to have both account ids

[D4G_fnc (D4G)]

(post deleted by author)

[D4G_fnc (D4G)]

Hey,

Could you clear the cache on my account as well? I’ve been dealing with this issue since September last year.

The first attached thread by OP is my forum report and includes the project ID, which you can use to find my account ID. If needed, I can also DM you my account ID.

[HeyPickledDave (Dave)]

@D4G_fnc please send me a DM with your account id
today is a US holiday so it’ll probably have to wait until tomorrow
I’ll keep you posted

[HeyPickledDave (Dave)]

As it turns out, we don’t have an established protocol for clearing that cache on behalf of other people’s account

However, you should be able to achieve the same goal by opening a different project or create a blank one and launching a session on it

That Clear Source Files Cache menu item will be available in the 40.00 release btw

[supreeeeemeeeee (SupremeUEFN)]

Great, Thanks Dave!!

[D4G_fnc (D4G)]

Hey Dave, i just tried your fix, and am still having the same problem, here is the projectID 434d75cc-4c54-ec73-a7b6-6cbe36516ff7

[HeyPickledDave (Dave)]

@D4G_fnc can you attach your UEFN log plz?

[D4G_fnc (D4G)]

LogNet: NotifyAcceptingChannel 4/Editor client ValkyrieBeaconClient_1
LogNet: Client accepting Editor channel
LogEOSSDK: LogEOSRTC: TickTracker Ticks have been delayed. TimePeriod=[10.075851s] TickIntervalThreshold=[40ms] MaxTickInterval=[1001ms] MaxExecutionTime=[1ms] TicksCount=[38] ExpectedTicksCount=[303]
LogEOSSDK: LogEOSRTC: TickTracker Ticks have been delayed. TimePeriod=[10.152204s] TickIntervalThreshold=[40ms] MaxTickInterval=[884ms] MaxExecutionTime=[1ms] TicksCount=[44] ExpectedTicksCount=[305]
LogValkyrie: FlowStep_ResolveSessionCandidates()
LogValkyrie: Error: FlowStep_ResolveSessionCandidates(): Candidate module [47f3a3a8-4d54-146e-b81d-519556a147fb] failed validation with error: [errors.com.epicgames.pre-processing.download_failure]
LogValkyrieFortniteEditorLiveEdit: Verbose: FValkyrieFortniteEditorLiveEdit::UploadEnd C:/Users/Documents/Team/blankprojectforbugfix/blankprojectforbugfix.uefnproject, Failed
LogValkyrieFortniteEditorLiveEdit: Verbose: FValkyrieFortniteEditorLiveEdit::SetUploadRequired 1
LogValkyrieFortniteEditorLiveEdit: Verbose: FValkyrieFortniteEditorLiveEdit::SetTrackingUploadRequired 0
LogValkyrieRequestManagerEditor: OnProjectSyncCompleted: C:/Users/

Documents/Team/blankprojectforbugfix/blankprojectforbugfix.uefnproject, Failed
LogValkyrieEditorAnalytics: Displaying Stats for Flow
LogValkyrieEditorAnalytics: =========================
LogValkyrieEditorAnalytics: Flow=Play
LogValkyrieEditorAnalytics: PlayFlow=16.351
LogValkyrieEditorAnalytics: ↳ PrepareProjectSourceData=3.956
LogValkyrieEditorAnalytics: ↳ UploadCookDownload=16.351
LogValkyrieEditorAnalytics: ↳ ValidationSessionInitializeContext=1.082
LogValkyrieEditorAnalytics: ↳ ValidationSessionRunLocalValidation=2.821
LogValkyrieEditorAnalytics: ↳ SyncWithContentService=0.700
LogValkyrieEditorAnalytics: ↳ UpdateProjectMetadata=0.226
LogValkyrieEditorAnalytics: ↳ InitSyncModules=0.578
LogValkyrieEditorAnalytics: ↳ StageProjectModules=0.237
LogValkyrieEditorAnalytics: ↳ GatherFilesForValidation=0.000
LogValkyrieEditorAnalytics: ↳ DownloadPublishedVerseFiles=0.185
LogValkyrieEditorAnalytics: ↳ ValidateProject=0.565
LogValkyrieEditorAnalytics: ↳ FindServer=1.424
LogValkyrieEditorAnalytics: ↳ MatchmakingToServer=0.557
LogValkyrieEditorAnalytics: ↳ ValidationSessionUploadCandidateSourceFiles=0.809
LogValkyrieEditorAnalytics: ↳ ValidationSessionCreateValidationSession=0.248
LogValkyrieEditorAnalytics: ↳ ValidationSessionCreateModuleVersions=11.098
LogValkyrieEditorAnalytics: ↳ ValidationSessionPruneScratchSpace=0.687
LogValkyrieEditorAnalytics: ↳ ValidationSessionResolveSessionCandidates=0.190
LogValkyrieEditorAnalytics: =================================
LogSlate: Window ‘Unable to Play’ being destroyed
Message dialog closed, result: Ok, title: Unable to Play, text: At least 1 module failed remote validation

[HeyPickledDave (Dave)]

ok, I just wanted to make sure it was due to the same errors.com.epicgames.pre-processing.download_failure error
I’ve relayed the information to colleagues with greater expertise in this area

[HeyPickledDave (Dave)]

@D4G_fnc any project you upload you get that same error? and that since September?

[ockulkarni18]

Hi @HeyPickledDave, facing the same issue. The project was created in early Jan but after yesterday’s update i’m not able to launch any sessions.

Tried reinstalling UEFN, Fortnite and epic launcher. Still the same.

[D4G_fnc (D4G)]

Yes, any project I upload on that specific account I get the same error, and yes, it started happening to me at the end of September 2025.

[qqe (S e Y ジ)]

---

Intermediate

• Stores temporary files used by UEFN during build and run.

• Safe to delete – UEFN will recreate it automatically.

• Delete it if you have build errors or slow performance.

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Saved

• Stores temporary settings and log files for your project.

• Safe to delete – but you might lose some minor settings.

• Delete it if UEFN is not working properly or shows errors.

  C:\Users\AppData\Local\UnrealEditorFortnite

Before deleting the files, close the UEFN engine, then delete the two folders.
Don’t worry, it’s a safe and proven method.
After that, try again and let me know if the problem is solved.