Configuration Error

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: The entry 'ScriptModule' has already been added.

Source Error:

<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>


This happens when the config for a virtual directory is already defined in the root web application


There are two ways you can fix this:

<remove name="ScriptModule" />

Alternatively you can stop the  the web.config inheritance to the the virtual directory.
by adding this to the parent web.config

    <location path="." inheritInChildApplications="false">
    <system.web>
    ...
    </system.web>
    </location>


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I also came upon this problem when trying to fix this issue:

Unable to cast object of type 'System.Web.Configuration.ScriptingAuthenticationServiceSection' to type 'System.Web.Configuration.ScriptingAuthenticationServiceSection'.

which led me to realise there were .NET 3.5 references in the parent application's web.config

I tried to remove this using:

    <location path="." inheritInChildApplications="false">
    <system.web>
    ...
    </system.web>
    </location>

the problem actually occured due to the 3.5 reference in the <configSections>