How to use custom errors on IIS with ASP.NET

Question

I have modified my web.config file in my asp.net web application so that I am showing a custom error page:

<configuration>
    <system.web>
       ...snip
        <customErrors mode="On" defaultRedirect="WebForms/ErrorPage.aspx">
          <error statusCode="404" redirect="WebForms/ErrorPageNotFound.aspx" />
        </customErrors>        
    </system.web>  
</configuration>

When I run the site on IIS I get the following error:

Error code: 0x800700b7
Config section 'system.web/customErrors' already defined. 
Sections must only appear once per config file. 
See the help topic <location> for exceptions

Clearly I have some config hierarchy at play here but I don't know which file I need to look at (I have 276 web.config files on my machine) - can someone point me in the right direction.

When I find the file can I just rem out the top level customErrors section or is this going to cause an issue for other web applications on the same machine that don't have customErrors defined?

Jupaol · Accepted Answer · 2012-07-25 09:39:34Z

That section should be modified on the root web.config

If you re receiving that error, maybe you have several web.config in sub-directories of your main application, you should start checking those to remove them

Clearly I have some config hierarchy at play here but I don't know which file I need to look at (I have 276 web.config files on my machine) - can someone point me in the right direction.

Why don't you simply use windows search to find documents containing the string customErrors

To enable Windows 7 advanced search:

http://answers.microsoft.com/en-us/windows/forum/windows_7-files/in-windows-7-i-want-to-search-for-all-files/aadfe1f1-4a33-406b-8e72-bb920efa4f30

Config files hierarchy

Global machine. <windir>\Microsoft.NET\Framework\<ver>\Config\Machine.config
Root Web config. <windir>\Microsoft.NET\Framework\<ver>\Config\Web.config
Website. <wwwroot>\Web.config
Web application. <wwwroot>|IIS Web Site path\<webapp>\Web.config
Folder. <wwwroot>|IIS Web Site path\<webapp>\<dir>\Web.config

And where do I find the root web.config there is nothing in c:\inetpub\wwwroot? I tried an advanced search but it didn't even find my applications web.config file (!)
I meant the root config file of your application. Any way, I updated my answer to show you the ASP.Net config hierarchy

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