Revision control fail: Bad index file.

Development Getting Started & Setup
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1

Hi Guys,

I have attached a picture of the error. I don’t know why I can’t turn on revision control in UEFN. The error: Bad index file.
I ran a file check in the directory, then reinstalled UEFN. The error is still there.
What should I do?

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bad1
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Thanks
Gábor

2
  1. Launch Unreal Editor for Fortnite.
  2. Edit → Editor Preferences → Plugins → Source Control
  3. Ensure “Git” is selected and that the “Path to Git executable” points to your Git install (e.g. C:\Program Files\Git\bin\git.exe).
  4. Click Enable, then Connect.

If still failing thn
Clone a fresh copy: If your project is hosted remotely, clone it anew:

git clone https://your.git.remote/YourRepo.git NewUEFNProject

Then open that in UEFN.
Check file permissions Make sure nothing in .git\index is marked read‑only or locked by another process.
Try a different folder: Sometimes Windows path–length limits or special characters can corrupt Git’s index. Move the project to something simple like C:\UEFNProject.

OR

This error means UEFN’s local Revision‑Control cache has become corrupted and can’t read its “mutable” (i.e. changeable) data store. You’ll need to wipe out the bad cache and let UEFN rebuild it. Here’s how:

1. Close UEFN completely

Before touching any cache files, make sure the editor (and the Epic Games Launcher) are shut down.

2. Remove your project’s local URC cache

  1. In Windows Explorer, go to your UEFN project folder (where your .umap and .uasset files live).

  2. Open the Saved folder, then SourceControl.

  3. Delete both the MutableStore and ImmutableStore subfolders (and any ConnectionCache files) inside there.

    This clears UEFN’s local Revision‑Control stores, which are the root of the “failed to load data from mutable store” errors ([Epic Developer Community Forums][1]).

3. (Optional) Wipe your global URC cache

If you still see issues, also delete the global cache:

  • Open %LocalAppData%\FortniteGame\Saved\SourceControl\ and remove its contents.

This ensures no stale data remains locked somewhere else on your machine.

4. Restart UEFN and re‑enable Revision Control

  1. Launch Unreal Editor for Fortnite.
  2. Open your project.
  3. Go to Unreal Revision Control in the toolbar (or Edit → Editor Preferences → Source Control).
  4. Ensure your Git/URC settings are correct and click Enable → Connect.
  5. Press Sync Latest (or in a PowerShell shell inside your project folder run urc2 project snapshot get to pull the latest snapshot)

UEFN will now download a fresh copy of your repository’s metadata, rebuilding both mutable and immutable stores.

5. If it still fails

  • Run as Administrator: Right‑click the Epic Games Launcher and UEFN executables → Run as administrator.
  • Shorten your path: Move the project to something like C:\UEFNProject in case Windows path‑length limits are interfering.
  • Clone a fresh project: Use the CLI to sync into a new folder (urc2 project snapshot get latest --output="C:\NewProject"), then open that instead.

Let me know if any of these steps hit snags!

3

Thank you for your help.
I did what I could, but for example, I don’t have “Edit → Editor Preferences → Source Control.”
However, I deleted what I could, and then I got this error:

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4

@Stanicz could you please try the steps I outlined here: Error "Branch does not exist" in Unreal Revision Control - #8 by gxg_work Though the error is different this should help you reset your the revision control state for the project.