Sharepoint- Internal Server Error

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C#

Visual-Studio

SharePoint

Hai,

I have a problem in creating Sharepoint websites. Whenever I am trying to create a new project in Visual Studio, it shows the url is not valid. I couldn't even run the central administration website also. It shows an error like "HTTP Error 500.19 - Internal Server Error". I think the visual studio cannot identify the server name. Should i have to change the port number or any other property in the inetmgr? The error summary is as shown below. Please help me to solve my problem.

Error Summary 
HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid.
Detailed Error Information
Module IIS Web Core 
Notification Unknown 
Handler Not yet determined 
Error Code 0x800700b7 
Config Error There is a duplicate 'system.web.extensions/scripting/webServices/jsonSerialization' section defined  
Config File \\?\C:\inetpub\wwwroot\wss\VirtualDirectories\80\web.config 
Requested URL http://localhost:25807/ 
Physical Path  
Logon Method Not yet determined 
Logon User Not yet determined 
 
Config Source
   32:         Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
   33:           <section name="jsonSerialization"
   34:             type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, 
 
Links and More InformationThis error occurs when there is a problem reading the configuration file for the Web server or Web application. In some cases, the event logs may contain more information about what caused this error. View more information »

Thank you....