problem in change version of .net frame work on the site

Question

hii have a web site that i changed the version of .net on asp.net setting from 2 to 4 , in fact i upgrade it
but a problem happened! the line in web.config has error and i had to remove it




<sectionGroup name="scripting"
        type="System.Web.Configuration.ScriptingSectionGroup,
        System.Web.Extensions, Version=3.5.0.0, Culture=neutral,
        PublicKeyToken=31BF3856AD364E35">




1. when i remove it, site loads correctly but my menu in the front of pages lost it's styles!!! it use some css styles. why this happens? how can i fix it? i didn't have changed any thing else in the site but my menu don't work correctly.


2. and the other problem that is happened (after remove above line from web.config) is in only one of my admin's pages, that it has this error :
please help me about this two problems. thanks in advance

Server Error in '/' Application.

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Parser Error

Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately. 

Parser Error Message: Only Content controls are allowed directly in a content page that contains Content controls.

Source Error: 

Line 1: ?

Source File: /admin/config.aspx  Line: 1 

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Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.272