error in load assembly

I have a website with security in SQL server 2012. I have change my settings in web.config but it fails

her is the webconfig code

<

connectionStrings>

    <

addname="SecuritySQL"connectionString="Data Source=STEFAGROSERVER2\STEFAGRO2012SQL; Integgrated Security=SSPI;Initial Catalog=aspnetdb" />

    <

addname="stefagroEntities"connectionString="metadata=res://*/admin.stefagromodel.csdl|res://*/admin.stefagromodel.ssdl|res://*/admin.stefagromodel.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=STEFAGROSERVER2\STEFAGRO2012SQL;initial catalog=stefagro;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework&quot;"providerName="System.Data.EntityClient" />

    <

addname="stefagroConnectionString2"connectionString="Data Source=STEFAGROSERVER2\STEFAGRO2012SQL;Initial Catalog=stefagro;Integrated Security=True"providerName="System.Data.SqlClient" />

  </

connectionStrings>

  <

system.web>

    <

membershipdefaultProvider="AspNetSQL2012MembershipProvider">

      <

providers>

        <

addname="AspNetSQL2012MembershipProvider"

type="System.Web.Security.SqlMembershipProvider,

             System.Web, Version=4.0.0.0, Culture=neutral,

             PubicKeyToken=b03f5f7f11d50a3a

"

connectionstringName="SecuritySQL"

enablePasswordRetrieval="False"

enablePasswordReset="true"

requiresQuestionAndAnswer="true"

applicationName="/"

requiresUniqueEmail="False"

passwordFormat="Hashed"

maxInvalidPasswordAttempts="5"

MinRequiredPasswordLength="7"

minRequiredNonalphnumericCharacters="1"

PasswordAttemptWindow="10"

passwordStrengthRegularExpression="" />

      </

providers>

    </

membership>

    <

roleManagerenabled="true"cacheRolesInCookie="true"cookieName=".ASPXROLES"cookieTimeout="30"cookiePath="/"cookieRequireSSL="false"cookieSlidingExpiration="true"cookieProtection="All"defaultProvider="AspNetSqlRoleProvider"createPersistentCookie="false"maxCachedResults="25">

      <

providers>

        <

clear />

        <

addconnectionStringName="SecuritySQL"applicationName="/"name="AspNetSqlRoleProvider"type="System.Web.Security.SqlRoleProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />

      </

providers>

    </

roleManager>

    <

compilationdebug="true"strict="false"explicit="true"targetFramework="4.0">

      <

assemblies>

        <

addassembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />

      </

assemblies>

    </

compilation>

    <

authenticationmode="Forms">

      <

formsloginUrl="~/Account/Login.aspx"timeout="2880" />

    </

authentication>

    <

profiledefaultProvider="DefaultProfileProvider">

      <

providers>

        <

addname="DefaultProfileProvider"type="System.Web.Providers.DefaultProfileProvider, System.Web.Providers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"connectionStringName="SecuritySQL"applicationName="/" />

      </

providers>

it say that it can't load assembly system.web

if anyone can give me a solution I will be happy

I use visual studio 2012 and started with a template

thanks

Stefan Groenen