Fiddler classic won't launch in Windows 11

[n/a]

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.

[n/a]

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.