Ajaxcontroltoolkit additionaluploadfileextensions where to position in web. Config file

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web.config

ASP.NET4

I need to be able to import .msg files with the ajaxToolkit:AjaxFileUpload control. I have read various articles saying that I need to add the following to my web.config file. 

    <ajaxControlToolKit additionalUploadFileExtensions="msg" />

I am not sure where to place it in the config file as where ever I try and add it I get the following error:

>HTTP Error 500.19 - Internal Server Error

>The requested page cannot be accessed because the related configuration data for the page is invalid.

This is my web config. Some bits are missing for security reasons


    <?xml version="1.0" encoding="utf-8"?>
    
    <configuration>
      <system.web>
        <compilation debug="true" targetFramework="4.6.1" />
        <httpRuntime targetFramework="4.6.1" />
        <sessionState mode="InProc" timeout="20" />
        <pages>
          <namespaces>
            <add namespace="System.Web.Optimization" />
          </namespaces>
          <controls>
            <add assembly="Microsoft.AspNet.Web.Optimization.WebForms" namespace="Microsoft.AspNet.Web.Optimization.WebForms" tagPrefix="webopt" />
          <add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" /></controls>
        </pages>
        <httpModules>
          <add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" />
        </httpModules>
        <customErrors mode="Off"></customErrors>
        <authentication mode="Windows"></authentication>
        <httpHandlers>
          <add verb="*" path="AjaxFileUploadHandler.axd"
            type="AjaxControlToolkit.AjaxFileUploadHandler, 
              AjaxControlToolkit"/>
        </httpHandlers>
      </system.web>
      <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
          <dependentAssembly>
            <assemblyIdentity name="Newtonsoft.Json" culture="neutral" publicKeyToken="30ad4fe6b2a6aeed" />
            <bindingRedirect oldVersion="0.0.0.0-10.0.0.0" newVersion="10.0.0.0" />
          </dependentAssembly>
          <dependentAssembly>
            <assemblyIdentity name="WebGrease" culture="neutral" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="0.0.0.0-1.6.5135.21930" newVersion="1.6.5135.21930" />
          </dependentAssembly>      
          <dependentAssembly>
            <assemblyIdentity name="System.Diagnostics.DiagnosticSource" publicKeyToken="cc7b13ffcd2ddd51" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-4.0.2.1" newVersion="4.0.2.1" />
          </dependentAssembly>
          <dependentAssembly>
            <assemblyIdentity name="Antlr3.Runtime" publicKeyToken="eb42632606e9261f" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-3.5.0.2" newVersion="3.5.0.2" />
          </dependentAssembly>
        </assemblyBinding>
      </runtime>
      <system.webServer>
        <validation validateIntegratedModeConfiguration="false" />
        <modules>
          <remove name="TelemetryCorrelationHttpModule" />
          <add name="TelemetryCorrelationHttpModule" type="Microsoft.AspNet.TelemetryCorrelation.TelemetryCorrelationHttpModule, Microsoft.AspNet.TelemetryCorrelation" preCondition="integratedMode,managedHandler" />
          <remove name="ApplicationInsightsWebTracking" />
          <add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" preCondition="managedHandler" />
        </modules>
      <handlers>
          <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
          <remove name="OPTIONSVerbHandler" />
          <remove name="TRACEVerbHandler" />
          <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
        <add name="AjaxFileUploadHandler" verb="*" path="AjaxFileUploadHandler.axd" type="AjaxControlToolkit.AjaxFileUploadHandler, AjaxControlToolkit" />
        </handlers>
      </system.webServer>
      <connectionStrings>
      </connectionStrings>
    
      <system.codedom>
        <compilers>
          <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.7.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" />
          <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.7.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" />
        </compilers>
      </system.codedom>
      <system.net>
        <mailSettings>
          <smtp deliveryMethod="Network">
          </smtp>
        </mailSettings>
      </system.net>
      <appSettings>
      </appSettings>
      <ajaxControlToolkit additionalUploadFileExtensions="msg" />
    
    </configuration>

What I have tried:

I have tried placing the required line in various places within the config file all resulting in the same error message