Failed to start Python backend

[juanpaexpedite]

Hi, it has to be a really great project but I'm stuck just from the start:

This is the log:

2026-03-05 19:12:45,911 - INFO - [Electron] Session log file: C:\Users\jpgc\AppData\Local\LTXDesktop\logs\session_2026-03-05_19-12-45_unknown.log
2026-03-05 19:12:45,935 - INFO - [Electron] [icon] Loading app icon from: C:\Program Files\LTX Desktop\resources\icon.ico | exists: false
2026-03-05 19:12:46,190 - INFO - [Renderer] Projects saved: 0
2026-03-05 19:12:46,191 - INFO - [Renderer] Starting Python backend...
2026-03-05 19:12:46,192 - INFO - [Electron] Using bundled Python: C:\Users\jpgc\AppData\Local\LTXDesktop\python\python.exe
2026-03-05 19:12:46,192 - INFO - [Electron] Starting Python backend: C:\Users\jpgc\AppData\Local\LTXDesktop\python\python.exe C:\Program Files\LTX Desktop\resources\backend\ltx2_server.py
2026-03-05 19:12:47,969 - INFO - [Backend] Log file: C:\Users\jpgc\AppData\Local\LTXDesktop\logs\session_2026-03-05_19-12-45_unknown.log
2026-03-05 19:12:48,039 - INFO - [Backend] SageAttention enabled - attention operations will be faster
2026-03-05 19:12:48,364 - INFO - [Electron] Python backend exited with code 1
2026-03-05 19:12:48,376 - ERROR - [Renderer] Failed to start Python backend: Error: Error invoking remote method 'start-python-backend': Error: Python backend exited during startup with code 1
2026-03-05 19:12:50,976 - INFO - [Electron] Checking for update...

I have Windows 11. Does the project use an specific Python version, uses a venv?

[plox-1]

same

[jjjuande]

I had the same error, then uninstall the app and remove the content in "C:\Users\jpgc\AppData\Local\LTXDesktop". Installed again, but installing it just for the current user and using a short install route like "C:\LTX", then it worked.

[plox-1]

OK I found a solution:

Right click LTX Desktop shortcut -> Start as administrator:

EDIT:
I believe it's because I choose "For all users (requires administrative permissions)" during installation, and then LTX Desktop did not start with administrative permissions. Just a guess.

[panbeep]

Running as administrator did not work. Any other ideas?

[LSI86]

At first, only the Python environment was installed, and then it reported the same error when starting... When I followed the advice and ran it as an administrator, I couldn't do anything: "This app is configured for API-only generation. Add your API key to continue." Even uninstalling it didn't help; it still only offers the API... Where is the application configuration stored so that it can be reconfigured? Even after uninstalling and reinstalling, it is still configured as before.

[caleboleary]

for me, the issue was a conflicting torchvision, I renamed the folder and it started

AppData\Roaming\Python\Python313\site-packages\torchvision -> AppData\Roaming\Python\Python313\site-packages\torchvision-bak

[CodeBarrie]

Root Cause Found

The crash happens at ltx2_server.py line 155-157:

OUTPUTS_DIR = Path(__file__).parent / "outputs"
OUTPUTS_DIR.mkdir(parents=True, exist_ok=True)

This tries to create an outputs/ directory inside C:\Program Files\LTX Desktop\resources\backend\, which requires admin privileges. Standard user processes can't write to Program Files.

The error (visible when running the backend manually):

PermissionError: [WinError 5] Access is denied: 'C:\Program Files\LTX Desktop\resources\backend\outputs'

The session log doesn't capture stderr, so you only see "exited with code 1" without the traceback. The last successful log line is "SageAttention enabled" because the PermissionError happens on the very next module-level statement.

Why the workarounds work

• Run as admin → process has write access to Program Files
• Install to C:\LTX → no restricted directory, user has write access

Suggested fix

OUTPUTS_DIR should use APP_DATA_DIR (which already resolves to AppData\Local\LTXDesktop) instead of Path(__file__).parent:

OUTPUTS_DIR = APP_DATA_DIR / "outputs"   # was: Path(__file__).parent / "outputs"

This is consistent with how MODELS_DIR is already handled on line 152.

Temporary workaround

Create the folder manually with write permissions (run in an admin terminal):

mkdir "C:\Program Files\LTX Desktop\resources\backend\outputs"
icacls "C:\Program Files\LTX Desktop\resources\backend\outputs" /grant Users:F

[xbobos]

I tried all the methods mentioned above, but the same error keeps occurring. (windows 11,rtx5090)

[jjjuande]

"This app is configured for API-only generation. Add your API key to continue."

LSI86 you need at least 31GB of free VRAM in order to be able to use in local mode. I hope than in a near future there's a version which uses quantized versions of the models, lowering the retirements.

[kexar]

The same for me - I tried all the methods mentioned above, but the same error keeps occurring. Windows 11.

[shenkhar]

Root cause

The bundled Python runtime used by LTX Desktop runs in isolated embedded mode due to the file:

C:\Users\<user>\AppData\Local\LTXDesktop\python\python313._pth

When a python._pth file exists, Python ignores the script directory and PYTHONPATH and only loads modules from paths explicitly listed in that file.

Because the backend folder was not listed, Python could not resolve:

from state.app_settings import AppSettings

even though the state package exists in:

H:\LTX\LTX Desktop\resources\backend\state

This caused the backend to crash on startup with:

ModuleNotFoundError: No module named 'state'

---

Workarounds / Fixes

Workaround 1 (recommended): Add backend path to python313._pth

Edit the embedded Python path file:

C:\Users\<user>\AppData\Local\LTXDesktop\python\python313._pth

PowerShell command:

@"
python313.zip
.

# Uncomment to run site.main() automatically
import site

Lib\site-packages
H:\LTX\LTX Desktop\resources\backend
"@ | Set-Content "C:\Users\<user>\AppData\Local\LTXDesktop\python\python313._pth"

Verify:

& "C:\Users\<user>\AppData\Local\LTXDesktop\python\python.exe" -c "import state; print(state.__file__)"

Expected output:

H:\LTX\LTX Desktop\resources\backend\state\__init__.py

---

Workaround 2: Disable isolated Python path

Rename the _pth file so Python returns to normal path behavior.

Rename-Item "C:\Users\<user>\AppData\Local\LTXDesktop\python\python313._pth" "python313._pth.bak"

Test:

& "C:\Users\<user>\AppData\Local\LTXDesktop\python\python.exe" "H:\LTX\LTX Desktop\resources\backend\ltx2_server.py"

---

Workaround 3: Patch ltx2_server.py

Add this at the top of:

H:\LTX\LTX Desktop\resources\backend\ltx2_server.py

import os
import sys

BACKEND_ROOT = os.path.dirname(os.path.abspath(__file__))
if BACKEND_ROOT not in sys.path:
    sys.path.insert(0, BACKEND_ROOT)

---

Verification

Confirm backend modules resolve correctly:

& "C:\Users\<user>\AppData\Local\LTXDesktop\python\python.exe" -c "import sys; [print(p) for p in sys.path]; import state; print(state.__file__)"

Then start the backend:

& "C:\Users\<user>\AppData\Local\LTXDesktop\python\python.exe" "H:\LTX\LTX Desktop\resources\backend\ltx2_server.py"

---

Recommended long-term fix

The Electron launcher should ensure the backend directory is on sys.path, either by:

• spawning Python with cwd = backend
• setting PYTHONPATH
• or explicitly inserting the backend root in ltx2_server.py

[xbobos]

Even after trying all the suggested methods above, the same error keeps occurring. It still can’t be resolved, even when using an LLM.

[munishbp]

Additional root cause: port 8000 conflict

After reinstalling to the per-user directory (AppData\Local\Programs\LTX Desktop) as suggested above, the backend
still crashed with exit code 1 — but now it got much further. The session log showed everything succeeding
(SageAttention, Models directory, GPU detection, full server banner) before silently dying:

[Backend] ============================================================
[Backend] LTX-2 Video Generation Server (FastAPI + Uvicorn)
[Backend] GPU: NVIDIA GeForce RTX 5090 | VRAM: 31 GB
[Backend] ============================================================
[Electron] Python backend exited with code 1

The actual error was that port 8000 was already in use by another process (ManagerService.exe → Manager.exe in my
case). When uvicorn tries to bind, it throws an OSError to stderr — which isn't captured by the session log formatter,
so the crash appears silent.

You can check with:
netstat -ano | findstr ":8000"

Fix: Patch app.asar to change the port (same byte length, safe for asar format):

asar = r"C:\Users<you>\AppData\Local\Programs\LTX Desktop\resources\app.asar"

with open(asar, "rb") as f:
data = f.read()

Backup

with open(asar + ".bak", "wb") as f:
f.write(data)

Patch port 8000 -> 9000

patched = data.replace(b"const Vc = 8e3", b"const Vc = 9e3", 1)

with open(asar, "wb") as f:
f.write(patched)

print("Done — restart LTX Desktop")

The Python backend automatically picks up the new port via the LTX_PORT env var that Electron passes to it. After
patching, the backend started successfully on port 9000.

This is a separate issue from the PermissionError and ModuleNotFoundError causes discussed above — you can hit this
even after fixing those. Worth noting this patch gets overwritten by auto-updates.

[Hikska]

Conflict with other Python packages on your system

If you have Python 3.13 installed separately on your PC, its packages can conflict with LTX Desktop's bundled ones. To fix this:

1. Press Win + R, type sysdm.cpl, press Enter
2. Go to Advanced tab → Environment Variables
3. Under User variables, click New
4. Name: PYTHONNOUSERSITE — Value: 1
5. Click OK everywhere
6. Restart Computer and launch LTX Desktop