Hi,
I keep getting this error message when starting Fiddler on Windows 7.
Fiddler appears to be running on this user account. Maybe in a terminal services session.
If you run two copies of fiddler at the same time, your settings may be corrupted.
Start Fiddler anyway? ( Yes/No buttons)
I was using a previous version, sorry didnt record which one but I tend to keep it faily up to date. I started Fiddler2Script Editor ( by mistake as it happens ) and nothing started. I then attempted to run Fiddler and nothing started. I assumed my windows was in a mess and rebooted. However the problem persists and no happens on every attemt to start Fiddler. I upgraded to 2.5.1.2 and still the problem persists.
Can anyone point me at a solution, or tell me what you need to know to assist in finding a solution please.
Windows Event Viewer does not show any obvious issues.
8 Answers, 1 is accepted
The error message and behavior in question suggest that either Fiddler is running in some other account (e.g. if someone else were logged into your computer) or, more likely, there's a problem with your computers ability to create a mutex (an object programs use to ensure they're only running once).
Unfortunately, troubleshooting this sort of problem is pretty tricky. What security or anti-virus software do you have installed? Do you have the latest updates for the .NET Framework from Microsoft installed? Is this PC a home PC or a work PC that is managed by a network administrator?
Thanks!
Eric Lawrence
Telerik
Rank 1
Hi Eric,
Anti Virus = AVG(Free)
PC is a W7 32bit desktop computer on a workgroup rather than a domain fully updated.
.NET =
Microsoft .NET Framework 4.5 Multi-Targeting Pack 4.5.50709
Microsoft .NET Framework 4.5 SDK 4.5.50709
Microsoft .NET Framework 4.5.2 4.5.51209
I am the only account active when the problem occurs and the account is an Administrator (password Protected)
Do you think an uninstall and reinstall of Fiddler would be of any use?
Is there any log file created by Fiddler ( I dont see one), or an option I can turn on to get one?
Does the problem continue if you disable AVG?
Is the account literally "Administrator" or is it another account with Admin permissions? If you go to a command prompt in the account and type whoami what does it return?
Uninstalling and reinstalling will not help.
There are many different logging options for Fiddler, but none of them will help here; this is nearly the very first call that Fiddler makes:
string sMutexName = (@"Global\FiddlerUser_" + Environment.UserName);
oMutex = new Mutex(false, sMutexName);
if (!oMutex.WaitOne(40, false)) {
// ... Fiddler is already running...
To debug this live, we'd need to trace execution on the machine in question to see why the underlying Mutex API is failing...
Regards,
Eric Lawrence
Telerik
Rank 1
That did it.
I disabled AVG, then ran Fiddler and it started without any issues.
Then I ran Fiddler2Script Editor, which ran without issues.
I then re-emabled AVG and now Fiddler and Fiddler2Script Editor run again without issues.
I am guessing AVG got a code update and either that or that fact that it got updated after the original issue cauesed the issue.
Thanks for pushing me in the right direction.
Rank 1
It appears to be something to do with AVG, and possibly specific to the recent update 2015.0.6081 as this did not happen until recently and I have been a user of AVG and Fiddler since version 1 days.
WORK AROUND:
In order to get Fiddler2 to run I have to disable AVG, run Fiddler2 and then re-enable AVG.
I have reported the issue to AVG. I dont hold out a lot of hope of them admitting a problem or supplying a quick fix.
I would be very interested to see if I was the only one having this issue, as if I am then its probably NOT specifically linked to AVG and I can start to look else where for a solution.
Eric, If you want to try a Trace Execution, let me know what is required at my end as I am more than willing to try if you think that will help.
I've confirmed that this is indeed a performance problem caused by AVG; they cause Fiddler's check for uniqueness to time out. You can safely ignore the warning.
I've contacted AVG to request help, and I'll hack a workaround into the next version.
https://twitter.com/ericlaw/status/618519996008796160
Thanks for the great issue report!
Eric Lawrence
Telerik
Rank 1
Well much to my surprise and probably more to do with your contacting them than me, the people at AVG sent me a SysInfo program to run to collect info from my PC along with some test instructions to disabling each component in turn to try and see which one was causing the issue.
Turns out that even with all components disabled the issue still occurs. Of course at apparently randon times Fiddler2 will start quite normally even with all AVG components running. So this is not going to be a quicky fix I dont think, but who knows!
To add more grist to the mill: I think I have just put 2 and 2 together and hopefully made 4.
I have been having odd problems over the last month or maybe 2 months where a browser ( all of them FF/IE/Chrome etc ) will suddenly hang and give the "Not Responding" message in the title bar. Left alone for long enough they normally jump back into action after 2 to 5 minutes. It occurred to me that this may also be being caused by whatever changes have been made to AVG. A friend who also uses AVG(Free) has also reported similiar problem to me ( ok, its the mother in law ).
Unfortunately the only way to test that is to remove AVG and install another AV, and as they appear to be attempting to solve the problem it would seem churlish to just up and move to another product at least until AVG have had a chance to fix it.
Anyway, many thanks for your assistance, and Fiddler!
Rank 1
I took AVG's offer of a remote support session. Just a first line support guy and the upshow was a workaround involving setting an exception on the fiddler2 exe.
However I did press the point that this was not a FIX and the guy promised to pass all the information to a real developer.
Well a few days later update 2015.0.6122 arrived. They obviously took this seriously and low and behold the issue seems to be fixed. I removed the AVG exception and Fiddler2 now starts normally again.
I also have not had any Browser "Not Responding" issues and Outlook has stopped hanging somewhere during multi email account downloads.
So well done AVG for a quick responce to this issue. Although quite possibly as it was effecting all sorts of things on a windows system the issue was already know about and being worked on. But lets look on the bright side, problem solved as far as I can tell.