Only one configSections element allowed per config file and if present must be the first child of the root configuration element

Question

I am developing the console application and when I run the .exe file, I get the following error:

system.Configuration.ConfigurationErrorsException: Only one <configSections> element allowed per config file and if present must be the first child of the root <configuration> element.

Here's my App.config file:

<configuration>
    <startup useLegacyV2RuntimeActivationPolicy="true">
        <supportedRuntime version="v4.0"/>
    </startup>
    <configSections>
        <section name="Reva.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
        <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
    </configSections>
    <!-- ... -->

However, if I remove the following startup section, then it works fine

<startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
</startup>

Absentminded

In German, the error message reads "Pro Konfigurationsdatei ist nur ein <configSections>-Element zulässig und muss, sofern vorhanden, das erste untergeordnete Element des Stamm-<configuration>-Elements sein." (Just in case, someone is googling this one). – Saratov

Answer 1

The error message itself actually details the correct fix:

configSections must be the first child* of the root element:

^{*emphasis added}

So just move the configSections to the top:

<configuration>
    <configSections>
        <section name="Reva.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
        <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
    </configSections>
    <startup useLegacyV2RuntimeActivationPolicy="true">
        <supportedRuntime version="v4.0"/>
    </startup>
</configuration>

Lohman

Today I learnt I should read the whole error message. Thanks. – Mathew

@AtronSeige me too :P – Zacatecas

I got the same error message for a windows service and the app.config doesn't even have a "<configSections>" tag in it. – Sperry

Please post your config to pastebin and Link it here – Lohman

As it turned out, my config was OK but the machine.config on that machine was broken. It even contained an SQLExpress/localhost connection string although no SQL was ever installed on that machine. – Sperry

If you rearranged configSections as first element and you still have same error then delete everything in "Solution/bin" folder and try again. – Monocot

Answer 2

The Error web.config File

 <?xml version="1.0" encoding="utf-8"?>   

<configuration>    
   <connectionStrings>   
      <add name="SQLConnect" 
           connectionString="Data Source=SAHIL; Initial Catalog=Demo; Integrated Security=SSPI" 
           providerName="System.Data.SqlClient" />   
   </connectionStrings>     

   <configSections>   
      <sectionnamesectionname="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, 
          Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" /> 
   </configSections>  

   :   
   :   
   :   
   :   
   :   
   :   
   :   
</configuration> 

The Error Was

To fix the error, I rearranged the elements and the error was fixed.

Type

Answer 3

For my case:

Below app.config was giving run time error as

"ConfigurationErrorsException: Only one <configSections> element allowed per config 
file and if present must be the first child of the root <configuration> element."

Faulty App.config:

<configuration> 
    <appSettings></appSettings>
    <configSections></configSections>   
    <startup> </startup>
    <runtime></runtime>
</configuration>

I just moved <configSections></configSections> on the top and problem resolved.

Correct App.config:

<configuration> 
    <configSections></configSections>
    <appSettings></appSettings>
    <startup> </startup>
    <runtime></runtime>
</configuration>

Osbourn