C# – MVC3 Type exists in two different assemblies

I'm getting an error when I run my MVC3 application.

i:\Dev\mvc3Project\Views\Shared\EditorTemplates\SelectListEnum.cshtml(13): error CS0433: The type 'mvc3Project.UI.HtmlExtensions.HtmlAssist' exists in both 'c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\fcb9f71c\d519c72a\assembly\dl3\b333487e\ed66abf6_51decb01\mvc3Project.DLL' and 'c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\fcb9f71c\d519c72a\App_Code.tfh8pvp4.dll'

I have tried deleting all the files in Temporary ASP.NET files.

The following two threads haven't helped
Thread 1
Thread 2

Here is my web.config. It's actually the default one VS creates for you.

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=152368
  -->

<configuration>
    <connectionStrings>
        <add name="ApplicationServices"
             connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true"
             providerName="System.Data.SqlClient" />

    </connectionStrings>

    <appSettings>
        <add key="ClientValidationEnabled" value="true"/>
        <add key="UnobtrusiveJavaScriptEnabled" value="true"/>
    </appSettings>

    <system.web>

        <globalization enableClientBasedCulture="true" uiCulture="auto" culture="auto" />

        <compilation debug="true" targetFramework="4.0">
            <assemblies>
                <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.Helpers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.WebPages, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
            </assemblies>
        </compilation>

        <!--<trace enabled="true" pageOutput="true" localOnly="true" traceMode="SortByCategory" />-->

        <machineKey decryption="AES" 
                    validation="HMACSHA512" 
                    validationKey="AutoGenerate" 
                    decryptionKey="ABAA84D7EC4BB56D75D217CECFFB9628809BDB8BF91CFCD64568A145BE59719F" />


        <authentication mode="Forms">
            <forms loginUrl="~/Account/LogOn" timeout="2880" />
        </authentication>

        <membership>
            <providers>
                <clear/>
                <add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices"
                     enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false"
                     maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10"
                     applicationName="/" />
            </providers>
        </membership>

        <profile>
            <providers>
                <clear/>
                <add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider" connectionStringName="ApplicationServices" applicationName="/" />
            </providers>
        </profile>

        <roleManager enabled="false">
            <providers>
                <clear/>
                <add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="ApplicationServices" applicationName="/" />
                <add name="AspNetWindowsTokenRoleProvider" type="System.Web.Security.WindowsTokenRoleProvider" applicationName="/" />
            </providers>
        </roleManager>

        <pages>
            <namespaces>
                <add namespace="System.Web.Helpers" />
                <add namespace="System.Web.Mvc" />
                <add namespace="System.Web.Mvc.Ajax" />
                <add namespace="System.Web.Mvc.Html" />
                <add namespace="System.Web.Routing" />
                <add namespace="System.Web.WebPages"/>
            </namespaces>
        </pages>
    </system.web>

    <system.webServer>
        <validation validateIntegratedModeConfiguration="false"/>
        <modules runAllManagedModulesForAllRequests="true"/>
    </system.webServer>

    <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            <dependentAssembly>
                <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
                <bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
            </dependentAssembly>
        </assemblyBinding>
    </runtime>
</configuration>

I don't have a copy of System.Web.Mvc in the bin folder either.

Any help would be appreciated.