I have been trying to resolve this issue.

I am using Windows 7 and VS2008 +iis7.5. My project is stuck because of this error.

The error says:

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    BeginRequest
Handler Not yet determined
Error Code  0x800700b7
Config Error    There is a duplicate 'system.web.extensions/scripting/scriptResourceHandler' section defined
Config File \\?\C:\inetpub\wwwroot\test23\web.config
Requested URL   http://localhost:80/test23
Physical Path   C:\inetpub\wwwroot\test23
Logon Method    Not yet determined
Logon User  Not yet determined
Config Source
   15:         <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
   16:          <section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
   17:           <sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
`

I followed the instructions in this Microsoft solution document, but it didn't help. http://support.microsoft.com/kb/942055