VS 2026 Error when running a .Net 10 console app in Debug

Question

VS 2026 Error when running a .Net 10 console app in Debug

Speckhals, Ken 0

User's image

Getting this error on a .Net 10 console app in VS 2026. I am just trying to run a basic console application with only Hello World in the Console. I haven't added anything to it. Can someone please help because VS 2026 is useless without being able to debug and I haven't found any issues and have uninstalled and reinstalled multiple times.

Thanks

Viorel 125.8K Reputation points

2025-12-19T22:44:29.9166667+00:00

Does it work without debugging (pressing <Ctrl+F5>)?

1 answer

Your answer

Viorel 125.8K Reputation points

2025-12-19T22:44:29.9166667+00:00

Does it work without debugging (pressing <Ctrl+F5>)?

Answer 1

Varsha Dundigalla(INFOSYS LIMITED) 4,215 Microsoft External Staff

Thank you for reaching out.

The dialog “A fatal error has occurred and debugging needs to be terminated. HRESULT=0x8013132d, ErrorCode=0x0” appears before your Hello World runs.

That means Visual Studio’s managed debugger couldn’t initialize or attach to the .NET runtime. This typically points to one of these environment issues (not your code):

A mismatch or incomplete install of .NET 10 SDK/targeting pack vs the debugger components in VS 2026.
Corrupted VS user caches/MEF composition or a third‑party extension breaking the debugger early.
Rarely: security software interfering with the attach, or custom launchSettings.json/project settings causing an early failure. Steps to fix
1. Try Safe Mode (quick isolation) Close VS → open Developer Command Prompt → run: devenv /safemode Create a new Console App (.NET 10) and press F5.
  - If it works in Safe Mode → an extension or cached state was the culprit. Disable non‑Microsoft extensions and go to Step 2.
2. Clear Visual Studio caches (safe to do) Close VS, then delete these folders (they’ll be rebuilt):
  - %LOCALAPPDATA%\Microsoft\VisualStudio\18.0\ComponentModelCache
  - %LOCALAPPDATA%\Microsoft\VisualStudio\Debugger Start VS normally, try F5 again.
3. Verify .NET 10 SDK/Runtime are really present In a terminal: dotnet --list-sdks dotnet --list-runtimes Ensure you see .NET 10 SDK and runtime entries.
  - If .NET 10 is missing or only previews show up → install/repair .NET 10 SDK and the .NET 10 targeting pack; then retry.
4. Retarget and keep the project simple In your .csproj, confirm: <TargetFramework>net10.0</TargetFramework> Temporarily remove launchSettings.json (if present), and use just: C#: Console.WriteLine("Hello World"); Console.ReadLine(); // keeps process alive during attach
5. Reset Visual Studio user data devenv /resetuserdata Reopen VS, create a fresh .NET 10 console app, press F5.
6. Repair workloads/components in VS Installer Open Visual Studio Installer → Modify:
  - Make sure “.NET desktop development” is installed.
  - Under Individual components, ensure .NET 10 runtime + .NET 10 targeting pack + .NET debugging tools are checked. Choose Repair, then retry.
7. Debugger options sanity check In Tools → Options → Debugging:
  - Uncheck “Enable Just My Code” for this test.
  - Ensure Symbol settings are default. In Project → Properties → Debug, set Debugger type = Managed (or Auto) and test F5.
8. Security software check (if corporate AV/EDR present) Temporarily disable aggressive script/behavior monitoring, or add exclusions for:
  - devenv.exe, vsdebugeng.exe, VsDebugConsole.exe Then try F5 again.
9. Collect the first failing clue (for escalation) Run: devenv /log Reproduce the crash, then open: %APPDATA%\Microsoft\VisualStudio\18.0\ActivityLog.xml The first error entry points to the exact component/extension to fix. References
- Visual Studio 2026 Release Notes (Debugging & diagnostics) – current features and fixes; repairing workloads/components is covered here https://learn.microsoft.com/en-us/visualstudio/releases/2026/release-notes
- Debugging techniques and tools (Visual Studio) – recommended practices, options, and how to collect useful diagnostics https://learn.microsoft.com/en-us/visualstudio/debugger/write-better-code-with-visual-studio?view=visualstudio

Please let us know if you require any further assistance, we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer". So that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

Speckhals, Ken 0

3	ERROR	Still unable to load MEF component DLL: Could not load file or assembly 'System.ClientModel, Version=1.7.0.0, Culture=neutral, PublicKeyToken=92742159e12e44c8' or one of its dependencies. The system cannot find the file specified. c:\program files\microsoft visual studio\18\professional\common7\ide\extensions\microsoft\copilotupgradeagent\Microsoft.UpgradeAssistant.Agents.dll			Microsoft.VisualStudio.ComponentModelHost.VsShellComponentModelHost	2025/12/22 16:19:59.396
3	ERROR	Still unable to load MEF component DLL: Could not load file or assembly 'System.ClientModel, Version=1.7.0.0, Culture=neutral, PublicKeyToken=92742159e12e44c8' or one of its dependencies. The system cannot find the file specified. c:\program files\microsoft visual studio\18\professional\common7\ide\extensions\microsoft\copilotupgradeagent\Microsoft.UpgradeAssistant.Agents.dll			Microsoft.VisualStudio.ComponentModelHost.VsShellComponentModelHost	2025/12/22 16:19:59.396

This is the error showing up in Activity Log. I have been using VS since 2005 and this is the first time I have ever installed a new VS and it broke right out of the box. I have uninstalled and reinstalled and followed all the directions that you gave me. This is a brand new console app with nothing added to it.

Speckhals, Ken 0 Reputation points

2025-12-22T16:27:19.5566667+00:00

It appears copilot which I don't want or use is causing the issue.
Varsha Dundigalla(INFOSYS LIMITED) 4,215 Reputation points Microsoft External Staff

2025-12-22T16:57:48.0533333+00:00
Thank you for reaching out.

Your understanding is correct.

The error you’re seeing is not related to your console app or .NET 10 code at all. The Activity Log clearly shows Visual Studio failing while loading a built‑in Microsoft extension (Copilot Upgrade Agent). That extension depends on an assembly called System.ClientModel (v1.7.0.0), and Visual Studio isn’t able to find it during startup.

When this happens, Visual Studio’s internal component system (MEF) doesn’t finish loading correctly. Because of that, the managed debugger never fully initializes, and Visual Studio immediately stops debugging with the fatal error before Hello World ever runs.

That also explains why:

It happens on a brand‑new console app

Re‑installing Visual Studio didn’t help

Clearing caches and repairing didn’t fix it

The issue happens even though you don’t use Copilot

Even if you don’t use Copilot, the Copilot Upgrade Agent still loads automatically, and if one of its required files is missing or mismatched, it can block debugging completely.

As a next step, could you please disable the Copilot Upgrade / Copilot‑related extension and then try debugging once?

Open Visual Studio → Extensions → Manage Extensions → Installed. Find “Copilot Upgrade Assistant / Copilot Upgrade Agent”, choose Disable, and restart Visual Studio. Then create/run a new .NET 10 Console app and press F5.

If debugging works after disabling it, that will confirm this is a Visual Studio extension dependency issue rather than anything in your project.

Please let us know if you require any further assistance, we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer". So that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.
Speckhals, Ken 0 Reputation points

2025-12-22T17:18:01.9933333+00:00

There is no Copilot Upgrade Assistant / Copilot Upgrade Agent in the installed packages.
Varsha Dundigalla(INFOSYS LIMITED) 4,215 Reputation points Microsoft External Staff

2025-12-23T07:57:12.0733333+00:00
Thank you for reaching out.
Copilot (including the Upgrade Assistant/agents) is built into Visual Studio 2026. It is not a separate package or extension, so you won’t see it in Installed Packages.

Where to disable it:

Open Visual Studio 2026

Go to Tools → Options

Select GitHub Copilot

Turn off the Copilot options

Click OK and restart Visual Studio

That’s the correct way to disable Copilot in VS 2026.

Please let us know if you require any further assistance, we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer". So that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.
Speckhals, Ken 0 Reputation points

2025-12-23T13:57:51.3266667+00:00

The underlying issue isn't copilot itself it is a broken VS 2026 debugger that fails to attach on a x64 or ANYCPU debug session. I found that you don't need to install copilot at all in the initial install. I reached out to Microsoft Technical support directly through Visual Studio. I am not the only one with this issue in my company. Thank you all for the help so far. If I find a solution I will post it.

Share via

VS 2026 Error when running a .Net 10 console app in Debug

1 answer

Your answer