CustomErrors mode="Off"

Question

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

32-bit

%windir%\Microsoft.NET\Framework\[version]\config\machine.config

64-bit

%windir%\Microsoft.NET\Framework64\[version]\config\machine.config 

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

"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)

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

<system.web>
   <customErrors mode="Off"/>
</system.web>

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".

For Sharepoint 2010 applications, you should also edit C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\web.config and define <customErrors mode="Off" />

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" />
    </customErrors>

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"

The one answer that actually worked to fix this I found here: https://stackoverflow.com/a/18938991/550975

Just add this to your web.config:

<configuration>  
  <system.webServer>  
    <httpErrors existingResponse="PassThrough"/>  
  </system.webServer>  
<configuration>

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 (http://msdn.microsoft.com/en-us/library/ms228298(VS.80).aspx).