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remove the changes that you made in web.config

In IIS, create a new Application Pool with target framework as 4.0.
In IIS, change your web-site to "application". For this, In IIS right click your website node in IIS and select "Convert to Application". Then select the Application Pool created in above step.

the best thisng to solve this problem is to that if now you are using vs2010 for projects which were made in framework 2.0 (using vs2008 or vs2005 ) add new web config from vs2010 and remove/exclude old webconfig. Add all connectionstring and other keys to new webconfig as in webconfig of framework 4.0 its much different from webconfig 2.0 framework.

or else you can do    <compilation debug="true" strict="false" explicit="true" targetFramework="2.0" />

I am making vs2010 projects using framework 4 . i am using code from older vs2008 projects but the files are all created in vs2010. I want to use .net 4

in my host panel i get IIS application pool disabled?

Please mention which IIS u r using IIS6 or IIS7 secondly pls paste your webconfig file here,

is your application running properly from vs2010 ??

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