how to solve Error cannot add duplicate collection entry of type add with unique key attribute 'value' in iis 7

Question

I created a asp.net website and published it in iis 7. I deleted the default website option in the iis 7 and created the new website in the iis 7. When i click the default document I got the error like "Error cannot add duplicate collection entry of type add with unique key attribute 'value' set to index.aspx". I used the following code in my web.config file.

<?xml version="1.0"?><configuration>
<configSections>
    <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
        <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
            <section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
            <sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
                <section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="Everywhere"/>
                <section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
                <section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
                <section name="roleService" type="System.Web.Configuration.ScriptingRoleServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
            </sectionGroup>
        </sectionGroup>
    </sectionGroup>
</configSections>
<appSettings/>
<connectionStrings/>
<system.web>
    <!-- 
        Set compilation debug="true" to insert debugging 
        symbols into the compiled page. Because this 
        affects performance, set this value to true only 
        during development.
    -->
    <compilation debug="true">
        <assemblies>
            <add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
            <add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
            <add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>

            <add assembly="System.Web.Extensions.Design, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add assembly="System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
            <add assembly="System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/></assemblies>
    </compilation>
    <!--
        The <authentication> section enables configuration 
        of the security authentication mode used by 
        ASP.NET to identify an incoming user. 
    -->
    <authentication mode="Windows"/>
    <!--
        The <customErrors> section enables configuration 
        of what to do if/when an unhandled error occurs 
        during the execution of a request. Specifically, 
        it enables developers to configure html error pages 
        to be displayed in place of a error stack trace.

    <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
        <error statusCode="403" redirect="NoAccess.htm" />
        <error statusCode="404" redirect="FileNotFound.htm" />
    </customErrors>
    -->
    <pages>
        <controls>
            <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        </controls>
    </pages>
    <httpHandlers>
        <remove verb="*" path="*.asmx"/>
        <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false"/>
    </httpHandlers>
    <httpModules>
        <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
    </httpModules>
</system.web>
<system.codedom>
    <compilers>
        <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
            <providerOption name="CompilerVersion" value="v3.5"/>
            <providerOption name="WarnAsError" value="false"/>
        </compiler>
    </compilers>
</system.codedom>
<!-- 
    The system.webServer section is required for running ASP.NET AJAX under Internet
    Information Services 7.0.  It is not necessary for previous version of IIS.
-->
<system.webServer>
    <validation validateIntegratedModeConfiguration="false"/>
    <modules>
        <remove name="ScriptModule"/>
        <add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
    </modules>
    <handlers>
        <remove name="WebServiceHandlerFactory-Integrated"/>
        <remove name="ScriptHandlerFactory"/>
        <remove name="ScriptHandlerFactoryAppServices"/>
        <remove name="ScriptResource"/>
        <add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
    </handlers>
<defaultDocument>
  <files>
    <remove value="default.aspx" />
    <remove value="index.html" />
    <remove value="iisstart.htm" />
    <remove value="index.htm" />
    <remove value="Default.asp" />
    <remove value="Default.htm" />
    <add value="index.aspx" />
  </files>
</defaultDocument>
<security>
  <requestFiltering>
    <requestLimits maxQueryString="5120"/>
  </requestFiltering>
</security>
</system.webServer>
<runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35"/>
            <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35"/>
            <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
        </dependentAssembly>
    </assemblyBinding>
</runtime>

Can anyone able help for that means its will really useful for my project. Thank you..

your configuration file seems to have some error, remove the suspicious entries one by one until you get it working. Some entries have the same value in a field which is supposed to be unique, the suspicious entries are those starting with — Davide Piras, Sep 17 '11 at 14:27

score 33 · Answer 1 · answered Sep 17 '11 at 14:56

IIS7 defines a defaultDocument section in its configuration files which can be found in the %WinDir%\System32\InetSrv\Config folder. Most likely, the file index.aspx is already defined as a default document in one of IIS7's configuration files and you are adding it again in your web.config.

I suspect that removing the line <add value="index.aspx" />

from the defaultDocument/files section will fix your issue.

The defaultDocument section of your config will look like:

<defaultDocument>
  <files>
    <remove value="default.aspx" />
    <remove value="index.html" />
    <remove value="iisstart.htm" />
    <remove value="index.htm" />
    <remove value="Default.asp" />
    <remove value="Default.htm" />
  </files>
</defaultDocument>

Note that index.aspx will still appear in the list of default documents for your site in the IIS manager.

For more information about IIS7 configuration, click here.

To be safe, you should have followed by . That way, if "index.aspx" has already been added at a higher level, you won't get the "cannot add duplicate collection entry" error. It seems odd that the element doesn't behave like an "upsert"---add if the entry does not already exist. But so it is. — Martin_W, Jan 04 '13 at 18:18

score 22 · Answer 2 · edited Nov 07 '17 at 03:44

22

All you need is a <clear /> tag. Here's an example:

<configuration>
  <system.webServer>
    <defaultDocument>
      <files>
        <clear />
        <add value="default.aspx" />
      </files>
    </defaultDocument>
  </system.webServer>
</configuration>

edited Nov 07 '17 at 03:44

Quill

2,729
1
33
44

answered Apr 09 '15 at 06:03

Gaurav Amatya

397
1
4
7

This issue happened to me as I edited Management >> Config Editor to set windowsauthentication to true and added some providers. For some reason, I wasn't seeing the windowsauthentication option appearing in IIS >> authentication. Then I found that I had to activate windowsauthentication on my web server. I did that and sure enough, the option appear in IIS >> authentication. So i felt I no longer needed to set this in Management >> Config Editor as my sites web.config would do it for me. Then I got this error. Using clear in my sites web.config worked but I feel i shouldn't have to do that... – Andy Jan 27 '16 at 11:36
This worked as a charm during migration to new IIS 10 – Yasskier Apr 04 '17 at 04:35

score 19 · Answer 3 · answered Jul 11 '12 at 06:59

The ideal scenario is to have <add value="default.aspx" /> in config so the application can be deployed to any server without having to reconfigure. IMHO I think the implementation within IIS is poor.

We've used the following to make our default document setup more robust and as a result more SEO friendly by using canonical URL's:

<configuration>
  <system.webServer>
    <defaultDocument>
      <files>
        <remove value="default.aspx" />
        <add value="default.aspx" />
      </files>
    </defaultDocument>
  </system.webServer>
</configuration>

Works OK for us.

score 8 · Answer 4 · answered Feb 18 '14 at 22:53

Remove element should clear out such errors. The reason behind this is the inherited settings. Your application will inherit some settings from its parent's config file and machine's (server) config files.
You can either remove such duplicates with the remove tag before adding them or make these tags non-inheritable in the upper level config files.

score 5 · Answer 5 · answered Jul 10 '14 at 11:38

Just keep the following in mind.

In IIS if you have a folder for example called Pages with multiple websites in it. Website will inherit settings from the web.config file from the parent directory. So even if the folder page (in this example Pages) isn't a website but contains a web.config file, all websites listed inside of it will inherit the setting.

score 0 · Answer 6 · answered Mar 21 '13 at 09:55

I got the same error and when I unknowingly removed all the default pages of the DefaultAppPool itself.

Resolution

I have clicked the DefaultAppPool and opened the Default Document. Then clicked on the Revert to Parent link on the Actions pane. The default documents have came again, and thus it solves the issue. I'm not sure this is the best way, but this one was the error which I have just met and hope to share with you. I hope this may help some one.

score 0 · Answer 7 · answered Dec 03 '19 at 10:30

For me in windows server 2012 R2 I solved it by removing the duplicates from web.config file i found this line duplicated twice i removed one line and kept the other line

<add name="CrystalImageHandler.aspx_GET" verb="GET" path="CrystalImageHandler.aspx" type="CrystalDecisions.Web.CrystalImageHandler, CrystalDecisions.Web, Version=13.0.4000.0, Culture=neutral, PublicKeyToken=692fbea5521e1304" preCondition="integratedMode"/></handlers><validation validateIntegratedModeConfiguration="false"/>

how to solve Error cannot add duplicate collection entry of type add with unique key attribute 'value' in iis 7

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