Fiddler classic won't launch in Windows 11

[Phil]

Having updated Windows 10 to 11, fiddler will no longer launch. 

I've tried uninstalling/reinstalling, but see the same effect.

The application event log shows the following pair of entries each time:

Faulting application name: Fiddler.exe, version: 0.0.0.0, time stamp: 0x00000000
Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000
Exception code: 0xc0000005
Fault offset: 0x0000000079b2a6dc
Faulting process ID: 0x3f6c
Faulting application start time: 0x01d8a0fe70d97aab
Faulting application path: C:\Users\XXXXX\AppData\Local\Programs\Fiddler\Fiddler.exe
Faulting module path: unknown
Report ID: d9f21a10-a4e4-4806-8ccd-6d4f797efb48
Faulting package full name: 
Faulting package-relative application ID: 

Faulting application name: Fiddler.exe, version: 0.0.0.0, time stamp: 0x00000000
Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000
Exception code: 0xc0000005
Fault offset: 0x000000002cf8a6dc
Faulting process ID: 0x4474
Faulting application start time: 0x01d8a0fe70d8e0fc
Faulting application path: C:\Users\XXXXX\AppData\Local\Programs\Fiddler\Fiddler.exe
Faulting module path: unknown
Report ID: 1556ffc4-1807-4032-b399-33a49dc42611
Faulting package full name: 
Faulting package-relative application ID: 

 

Bright ideas?

[Nick Iliev]

Try to uninstall and completely clean any remaining files (for example, while using a tool like CCleaner). Ensure that the folder C:\Users\iliev\AppData\Local\Programs\Fiddler is completely removed after the cleanup and is not being locked by some process. Then download (official link: https://www.telerik.com/download/fiddler ), then retry the installation. After successful installation, try to run Fiddler as an administrator.

[Phil]

Thanks for the suggestion...

I tried it, but I still get the same effect (whether running as administrator or not).

[Nick Iliev]

We tested on several different Windows 11 build machines, but so far, we cannot reproduce the issue locally. This leads us to conclude that there must be a specific local condition that causes the problem.

The error you see in the event log is Access Violation Error. This error could be related to issues like compatibility, memory conflicts, memory failure or lockup, malware, limited access to the Windows OS registry, etc. Check this article for more details explanations of what could produce that error and for some possible solutions.

Mainly, check and verify that you have enough free RAM allocated, that you don't have hardware issues related to the RAM, and that no third-party tools like antiviruses prevent Fiddler Everywhere's start.

[Szabi]

Having the exact same issue on Windows 11 (updated from Windows 10).

Fiddler everywhere gets stuck on the splash screen.

 

[Nick Iliev]

Hey Szabi,

Try the above suggestions, and check if you need to install a newer version of Windows 11 (you can check your current version by running the winver command in the OS run prompt). Also, consult your network administrator and ensure no security tools (including firewalls, zero-trust tooling, defenders, antivirus programs, etc.) are blocking the installation and usage of Fiddler Classic. You can also use an exception tool to further investigate what causes the access memory violation error code (e.g., as suggested in this SO thread)

 

[Szabi]

Hi Nick,

Thanks for your prompt response, I forgot to specify that the issue I am facing is with Fiddler Everywhere. I did all those that you mentioned (aside from the exception tool).

This is where it gets stuck:

This is what the process managers shows:

Fiddler Classic and other HTTP monitoring tools work. It's just Fiddler Everywhere that has this issue.

[Nick Iliev]

Thanks for clarifying that you are using Fiddler Everywhere instead of Fiddler Classic (the product initially discussed in this thread). Can you also confirm that you are hitting the same issue by posting the output of the Windows application event log (so that we can compare the exception code)?

Note that some Electron-based applications are failing with that exception code - users have reported a specific issue related to reinstalling the application while using the same installer (discussed here). Try to resolve the issue through the following flow:

1. Stop the Fiddler Everywhere application and uninstall it completely. If possible, use a tool like CCleaner to cleanly uninstall it from Windows registries.

2. Delete the previously downloaded Fiddler Everywhere installer.

3. Download the Fiddler Everywhere installer once more from the official download page at https://www.telerik.com/download/fiddler-everywhere 

4. Reinstall the application.

If the above doesn't resolve the issue then please provide the Windows event application logs related to the Fiddler Everywhere startup, and also send us any Fiddler Everywhere application logs (if such are available). Note that the logs can contain sensitive private information, so consider opening a private support ticket through the Telerik Support Center.