CustomErrors mode=”Off”

I get an error everytime I upload my webapp to the provider. Because of the customErrors mode, all I see is the default “Runtime error” message, instructing me to turn off customErrors to view more about the error.

Exasperated, I’ve set my web.config to look like this:

<?xml version="1.0"?>
        <customErrors mode="Off"/>

And still, all I get is the stupid remote errors page with no useful info on it.
What else can I do to turn customErrors OFF ?!


Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

This has been driving me insane for the past few days and couldn’t get around it but have finally figured it out:

In my machine.config file I had an entry under <system.web>:

<deployment retail="true" />

This seems to override any other customError settings that you have specified in a web.config file, so setting the above entry to:

<deployment retail="false" />

now means that I can once again see the detailed error messages that I need to.

The machine.config is located at





Hope that helps someone out there and saves a few hours of hair-pulling.

Method 2

“Off” is case-sensitive.

Check if the “O” is in uppercase in your web.config file, I’ve suffered that a few times (as simple as it sounds)

Method 3

In the interests of adding more situations to this question (because this is where I looked because I was having the exact same problem), here’s my answer:

In my case, I cut/pasted the text from the generic error saying in effect if you want to see what’s wrong, put

   <customErrors mode="Off"/>

So this should have fixed it, but of course not! My problem was that there was a <system.web> node several lines above (before a compilation and authentication node), and a closing tag </system.web> a few lines below that. Once I corrected this, OK, problem solved. What I should have done is copy/pasted only this line:

<customErrors mode="Off"/>

This is from the annals of Stupid Things I Keep Doing Over and Over Again, in the chapter entitled “Copy and Paste Your Way to Destruction”.

Method 4

For Sharepoint 2010 applications, you should also edit C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions14TEMPLATELAYOUTSweb.config and define <customErrors mode="Off" />

Method 5

I tried most of the stuff described here. I was using VWD and the default web.config file contained:

    <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
        <error statusCode="403" redirect="NoAccess.htm" />
        <error statusCode="404" redirect="FileNotFound.htm" />

I changed mode=”RemoteOnly” to mode=”Off”. Still no joy.
I then used IIS manager, properties, ASP.Net Tab, Edit configuration, then chose the CustomeErrors tab. This still showed RemoteOnly. I changed this to Off and finally I could see the detailed error messages.

When I inspected the web.config I saw that there were two CustomErrors nodes in the system.web; and I have just noticed that the second entry (the one I was changing was inside a comment). So try not to use notepad to inspect web.config on a remote server.

However, if you use the IIS edit configuration stuff it will complain about errors in the web.config. Then you can rule out all of the answers that say “is there an XML syntax error in your web.config”

Method 6

The one answer that actually worked to fix this I found here:

Just add this to your web.config:

    <httpErrors existingResponse="PassThrough"/>  

Method 7

You can generally find more information regarding the error in the Event Viewer, if you have access to it. Your provider may also have prevented custom errors from being displayed at all, by either overriding it in their machine.config, or setting the retail attribute to true (

Method 8

My problem was that i had this defined in my web.config

<httpErrors errorMode="Custom" existingResponse="Replace">
  <remove statusCode="404" />
  <remove statusCode="500" />
  <error statusCode="404" responseMode="ExecuteURL" path="/Error/NotFound" />
  <error statusCode="500" responseMode="ExecuteURL" path="/Error/Internal" />

Method 9

I also had this problem, but when using Apache and mod_mono. For anyone else in that situation, you need to restart Apache after changing web.config to force the new version to be read.

Method 10

If you’re still getting that page, it’s likely that it’s blowing up before getting past the Web.Config

Make sure that ASP.Net has permissions it needs to things like the .Net Framework folders, the IIS Metabase, etc. Do you have any way of checking that ASP.Net is installed correctly and associated in IIS correctly?

Edit: After Greg’s comment it occured to me I assumed that what you posted was your entire very minimal web.config, is there more to it? If so can you post the entire web.config?

Method 11

Actually, what I figured out while hosting my web app is the the code you developed on your local Machine is of higher version than the hosting company offers you. If you have admin privileges you may be able to change the Microsoft ASP.NET version support under web hosting setting

Method 12

We had this issue and it was due to the IIS user not having access to the machine config on the web server.

Method 13

We also ran into this error and in our case it was because the application pool user did not have permissions to the web.config file anymore. The reason it lost its permissions (everything was fine before) was because we had a backup of the site in a rar file and I dragged a backup version of the web.config from the rar into the site. This seems to have removed all permissions to the web.config file except for me, the logged on user.

It took us a while to figure this out because I repeatedly checked permissions on the folder level, but never on the file level.

Method 14

I had the same issue but found resolve in a different way.

What I did was, I opened Advanced Settings for the Application Pool in IIS Manager.

There I set Enable 32-Bit Applications to True.

Method 15

Try restarting the application (creating an app_offline.htm than deleting it will do) and if you still get the same error message, make sure you’ve only declared customErrors once in the web.config, or anything like that. Errors in the web.config can have some weird impact on the application.

Method 16

Do you have any special character like æøå in your web.config? If so make sure that the encoding is set to utf-8.

Method 17

Is this web app set below any other apps in a website’s directory tree? Check any parent web.config files for other settings, if any. Also, make your your directory is set as an application directory in IIS.

Method 18

If you’re using the MVC preview 4, you could be experiencing this because you’re using the HandleErrorAttribute. The behavior changed in 5 so that it doesn’t handle exceptions if you turn off custom errors.

Method 19

You can also try bringing up the website in a browser on the server machine. I don’t do a lot of ASP.NET development, but I remember the custom errors thing has a setting for only displaying full error text on the server, as a security measure.

Method 20

I have just dealt with similar issue. In my case the default site version was 1.1 while i was trying to start up a 2.0 web app. The error was pretty trivial, but it was not immediately clear why the custom errors would not go away, and runtime never wrote to event log. Obvious fix was to match the version in Asp.Net tab of IIS.

Method 21

Also make sure you’re editing web.config and not website.config, as I was doing.

Method 22

I have had the same problem, and the cause was that IIS was running ASP.NET 1.1, and the site required .NET 2.0.

The error message did nothing but throw me off track for several hours.

Method 23

Make sure you add

right after the system.web

I put it toward the end of the node and didn’t work.

Method 24

If you are doing a config transform, you may also need to remove the following line from the relevant web.config file.

<compilation xdt:Transform="RemoveAttributes(debug)" />

Method 25

Having tried all the answers here, it turned out that my Application_Error method had this:


Removing these lines and setting fixed the problem. (The client still got redirected to the error page with customErrors="On").

Method 26

I have had the same problem, and I went through the Event viewer application log where it clearly mention due to which exception this is happened. In my case exception was as below…

Exception information :

Exception type: HttpException 
Exception message: The target principal name is incorrect.  Cannot generate SSPI context.
at System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app)
at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context)
at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context)
at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext)

The target principal name is incorrect.  Cannot generate SSPI context.

I have just updated my password in application pool and it works for me.

Method 27

It’s also possible in some cases that web.config is not formatted correctly. In that case you have to go through it line by line before will work. Often, rewrite rules are the culprit here.

Method 28

That’s really strange. I got this error and after rebooting of my server it disappeared.

Method 29

For me it was an error higher up in the web.config above the system.web.

the file blah didn’t exist so it was throwing an error at that point. Because it hadn’t yet got to the System.Web section yet it was using the server default setting for CUstomErrors (On)

Method 30

None of those above solutions work for me. my case is

i have this in my web.config

<log4net debug="true">

either remove all those or go and read errors logs in your application folderlogs
eg.. C:UsersYourNamesourcereposYourProjectFolderlogs

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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