Arduino IDE 2.x.x stuck at start up

Development Tools IDE 2.x
1

Hello,

i am haveing problem to start the Arduino IDE 2.x.x.
It stucks at startup and i launched Powershell window in the Arduino Folder and i got the following:

2026-06-11T14:19:00.217Z daemon INFO Daemon is running.
2026-06-11T14:19:00.240Z root ERROR Uncaught Exception:  Error: 14 UNAVAILABLE: No connection established. Last error: read ECONNRESET (2026-06-11T14:19:00.238Z)
2026-06-11T14:19:00.240Z root ERROR Error: 14 UNAVAILABLE: No connection established. Last error: read ECONNRESET (2026-06-11T14:19:00.238Z)

If someone knows how to fix it, please write the solution.
Thanks

2

You will need to post the entire log in a code block so somebody can look at it.

3 
Arduino IDE 2.3.10
Checking for frontend application configuration customizations. Module path: C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\electron-main.js, destination 'package.json': C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\package.json
Setting 'theia.frontend.config.appVersion' application configuration value to: "2.3.10" (type of string)
Setting 'theia.frontend.config.cliVersion' application configuration value to: "1.5.1" (type of string)
Setting 'theia.frontend.config.buildDate' application configuration value to: "2026-06-09T16:48:46.639Z" (type of string)
Frontend application configuration after modifications: {"applicationName":"Arduino IDE","defaultTheme":{"light":"arduino-theme","dark":"arduino-theme-dark"},"defaultIconTheme":"none","electron":{"windowOptions":{},"showWindowEarly":true,"splashScreenOptions":{},"uriScheme":"arduino-ide"},"defaultLocale":"","validatePreferencesSchema":false,"reloadOnReconnect":true,"uriScheme":"theia","preferences":{"window.title":"${rootName}${activeEditorShort}${appName}","files.autoSave":"afterDelay","editor.minimap.enabled":false,"editor.tabSize":2,"editor.scrollBeyondLastLine":false,"editor.quickSuggestions":{"other":false,"comments":false,"strings":false},"editor.maxTokenizationLineLength":500,"editor.bracketPairColorization.enabled":false,"breadcrumbs.enabled":false,"workbench.tree.renderIndentGuides":"none","explorer.compactFolders":false},"appVersion":"2.3.10","cliVersion":"1.5.1","buildDate":"2026-06-09T16:48:46.639Z"}
Starting backend process. PID: 14924
Showing main window early
Using browser-only version of superagent in non-browser environment
Configuration directory URI: 'file:///c%3A/Users/khalilm/.arduinoIDE'
Configuring to accept webviews on '^.+\.webview\..+$' hostname.
2026-06-12T05:12:50.199Z root INFO Backend u.initialize: 32.3 ms [Finished 0.746 s after backend start]
2026-06-12T05:12:50.202Z root INFO Backend Object.initialize: 30.2 ms [Finished 0.746 s after backend start]
2026-06-12T05:12:50.202Z root INFO Backend a.initialize: 1.9 ms [Finished 0.746 s after backend start]
2026-06-12T05:12:50.202Z root INFO Backend a.initialize: 1.5 ms [Finished 0.746 s after backend start]
2026-06-12T05:12:50.202Z root INFO Backend u.initialize: 1.8 ms [Finished 0.747 s after backend start]
2026-06-12T05:12:50.204Z root INFO Backend l.initialize: 31.9 ms [Finished 0.748 s after backend start]
2026-06-12T05:12:50.210Z root INFO configured all backend app contributions
2026-06-12T05:12:50.211Z root INFO Backend l.onStart: 1.1 ms [Finished 0.759 s after backend start]
2026-06-12T05:12:50.212Z root INFO Backend d.onStart: 0.2 ms [Finished 0.760 s after backend start]
2026-06-12T05:12:50.213Z root INFO Backend a.onStart: 0.4 ms [Finished 0.760 s after backend start]
2026-06-12T05:12:50.213Z config INFO >>> Initializing CLI configuration...
2026-06-12T05:12:50.213Z root INFO Backend x.onStart: 0.6 ms [Finished 0.761 s after backend start]
2026-06-12T05:12:50.213Z config INFO Loading CLI configuration from c:\Users\khalilm\.arduinoIDE\arduino-cli.yaml...
2026-06-12T05:12:50.214Z daemon INFO Starting daemon from C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\resources\arduino-cli.exe...
2026-06-12T05:12:50.214Z root INFO Backend w.onStart: 0.8 ms [Finished 0.762 s after backend start]
2026-06-12T05:12:50.214Z discovery-log INFO start
2026-06-12T05:12:50.214Z discovery-log INFO start new deferred
2026-06-12T05:12:50.214Z root INFO Backend v.onStart: 0.4 ms [Finished 0.762 s after backend start]
2026-06-12T05:12:50.214Z root INFO Backend a.onStart: 0.2 ms [Finished 0.763 s after backend start]
2026-06-12T05:12:50.333Z root INFO Theia app listening on http://127.0.0.1:59948.
2026-06-12T05:12:50.333Z root INFO Finished starting backend application: 118.7 ms [Finished 0.881 s after backend start]
Restoring workspace roots: c:\Users\khalilm\Desktop\TB4\TB4_Quellcode\TB4_Software_Working_Version_002\TB4_Software_Working_Version_002.ino
2026-06-12T05:12:50.334Z root WARN The local plugin referenced by local-dir:/c%3A/Users/khalilm/.arduinoIDE/plugins does not exist.
2026-06-12T05:12:50.334Z root WARN The local plugin referenced by local-dir:/c%3A/Users/khalilm/.arduinoIDE/deployedPlugins does not exist.
2026-06-12T05:12:50.334Z root WARN The local plugin referenced by local-dir:C:\Users\khalilm\.arduinoIDE\plugins does not exist.
2026-06-12T05:12:50.345Z config INFO Loaded CLI configuration: {"board_manager":{"additional_urls":[]}}
2026-06-12T05:12:50.345Z config INFO Loading fallback CLI configuration to get 'directories.data' and 'directories.user'
isTempSketch: false. Input was c:\Users\khalilm\Desktop\TB4\TB4_Quellcode\TB4_Software_Working_Version_002\TB4_Software_Working_Version_002.ino
2026-06-12T05:12:50.500Z daemon INFO time="2026-06-12T07:12:50+02:00" level=info msg="arduino-cli version 1.5.1"
2026-06-12T05:12:50.510Z daemon INFO time="2026-06-12T07:12:50+02:00" level=info msg="Using config file: c:\\Users\\khalilm\\.arduinoIDE\\arduino-cli.yaml"
time="2026-06-12T07:12:50+02:00" level=info msg="Executing `arduino-cli daemon`"
2026-06-12T05:12:50.512Z root INFO Resolve plugins list: 296.1 ms [Finished 1.060 s after backend start]
2026-06-12T05:12:50.530Z daemon INFO Daemon überwacht jetzt 127.0.0.1: 59949
{"IP":"127.0.0.1","Port":"59949"}
2026-06-12T05:12:50.531Z daemon INFO Daemon is running.
2026-06-12T05:12:50.560Z root ERROR Uncaught Exception:  Error: 14 UNAVAILABLE: No connection established. Last error: Protocol error (2026-06-12T05:12:50.558Z)
2026-06-12T05:12:50.560Z root ERROR Error: 14 UNAVAILABLE: No connection established. Last error: Protocol error (2026-06-12T05:12:50.558Z)
    at t.callErrorFromStatus (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:3120866)
    at Object.onReceiveStatus (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6723244)
    at Object.onReceiveStatus (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:2604626)
    at Object.onReceiveStatus (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:2604071)
    at C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:4353123
    at process.processTicksAndRejections (node:internal/process/task_queues:77:11)
for call at
    at s.makeUnaryRequest (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6722775)
    at s.create (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:3119959)
    at instance (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6328952)
    at new Promise (<anonymous>)
    at y.createClient (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6328929)
    at y.create (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6327837)
    at C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:6326733
    at C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:1050883
    at s.invoke (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:1050973)
    at a.fire (C:\Users\khalilm\AppData\Local\Programs\Arduino IDE\resources\app\lib\backend\main.js:2:1052776)
2026-06-12T05:12:50.805Z config INFO Loaded fallback CLI configuration: {"directories":{"user":"H:\\Documents\\Arduino","data":"C:\\Users\\khalilm\\AppData\\Local\\Arduino15"}}
2026-06-12T05:12:50.805Z config INFO Merged CLI configuration with the fallback: {"directories":{"user":"H:\\Documents\\Arduino","data":"C:\\Users\\khalilm\\AppData\\Local\\Arduino15"},"board_manager":{"additional_urls":[]}}
2026-06-12T05:12:50.805Z config INFO Loaded the CLI configuration.
2026-06-12T05:12:51.044Z config INFO Mapped the CLI configuration: {"dataDirUri":"file:///c%3A/Users/khalilm/AppData/Local/Arduino15","sketchDirUri":"file:///h%3A/Documents/Arduino","additionalUrls":[],"network":"none","locale":"en"}
2026-06-12T05:12:51.044Z config INFO Validating the CLI configuration...
2026-06-12T05:12:51.050Z config INFO The CLI config is valid.
2026-06-12T05:12:51.050Z config INFO <<< Initialized the CLI configuration.
2026-06-12T05:12:51.908Z root INFO creating connection for 1
2026-06-12T05:12:53.039Z root WARN Frontend a.configure took longer than the expected maximum 100 milliseconds: 149.5 ms [Finished 2.622 s after frontend start]
2026-06-12T05:12:53.086Z root WARN A command editor.action.toggleStickyScroll is already registered.
Opening channel for service path '/services/electron-window'.
Opening channel for service path '/services/ide-updater'.
2026-06-12T05:12:53.249Z root INFO Start frontend contributions: 441.4 ms [Finished 2.814 s after frontend start]
2026-06-12T05:12:53.250Z root INFO Changed application state from 'init' to 'started_contributions'.
2026-06-12T05:12:53.265Z root INFO Changed application state from 'started_contributions' to 'attached_shell'.
2026-06-12T05:12:53.265Z root INFO >>> Restoring the layout state...
2026-06-12T05:12:55.124Z root INFO Deploy plugins list: 4908.4 ms [Finished 5.672 s after backend start]
2026-06-12T05:12:55.132Z root INFO [d6f9512b-39e5-474e-a2e6-0075059cb879] Waiting for backend deployment: 1905.2 ms [Finished 4.712 s after frontend start]
2026-06-12T05:12:55.622Z root INFO [hosted-plugin: 1716] PLUGIN_HOST(1716) starting instance
[Object: null prototype] {}
2026-06-12T05:12:56.191Z root INFO [d6f9512b-39e5-474e-a2e6-0075059cb879] Sync of 23 plugins: 1063.8 ms [Finished 5.775 s after frontend start]

This is all.

5

Anything special about your network setup? I could find a number of topics with the same error message: https://forum.arduino.cc/search?q=%23development-tools%3Aide-2-x%20root%20ERROR%20Error%3A%2014%20UNAVAILABLE%3A%20No%20connection%20established.%20Last%20error%3A%20Protocol%20error

E.g.

  1. Student linux laboratory - IDE 2.x won't start without internet connection - #6 by ptillisch which refers to proxy settings.
  2. IDE stuck on pulsating logo, yet another case
6

Yes, i suspect it's due to the proxy settings.
But i can not change that my self, i do not have admin rights (Work PC) od i do not know how.

7

Talk to your IT department. If you need this for work it should not pose a problem; if you need this for private use it might be another story. But the IT department might be flexible and allow it.