How can I solve this problem? : The configuration section 'system.web.extensions' cannot be read because it is missing a section declaration

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ASP.NET

web.config

I have a problem when I have uploaded my web application to webserver & the error is like this:

The configuration section 'system.web.extensions' cannot be read because it is missing a section declaration

& When I visit that pages it shows "500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed." this error...

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <system.web.extensions>
    <scripting>
      <webServices>
        <jsonSerialization maxJsonLength="500000000"/>
      </webServices>
    </scripting>
  </system.web.extensions>

  <system.net>
    <mailSettings>
      
     
    </mailSettings>
  </system.net>
  
  <connectionStrings>
    
  </connectionStrings>
  <system.web>
    <trust level="Full"/>
    <securityPolicy>
      <trustLevel name="Full" policyFile="internal"/>
    </securityPolicy>
    <compilation debug="true" targetFramework="4.0">
      <assemblies>
        <add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
        <add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
        <add assembly="mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
      </assemblies>
    </compilation>
    <pages>
      <controls>
        <add src="~/UserControls/Chart.ascx" tagName="Chart" tagPrefix="MAS"/>
      </controls>
    </pages>
  </system.web>
  <system.serviceModel>
    <bindings/>
    <client/>
  </system.serviceModel>
</configuration>

Please help me to resolve this error......