Issue with System.Web.WebPages after installing MVC4 - asp.net-mvc-3

Question

I have installed MVC4 and an MVC3 app that I have is now causing me problems. I get the error :
Could not load file or assembly 'System.Web.WebPages, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference
However, I cannot find any references in my code to v2 of WebPages, and I am wondering why I am getting this error. Can anybody help?
EDIT : Here is the full stack trace :
[FileLoadException: Could not load file or assembly 'System.Web.WebPages, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
ljMVC.Helpers.EditableHelpers.Editable(HtmlHelper helper, String htmlElement, String cssId, String defaultContent, Object htmlAttributes) in C:\Users\M\Desktop\Development\ASP.NET projects\ljMVC\ljMVC\ljMVC\Helpers\EditableHelpers.cs:90
ASP._Page_Areas_Gameplan_Views_MainGP_Index_cshtml.Execute() in e:\web\lovelyjubbl\htdocs\Areas\Gameplan\Views\MainGP\Index.cshtml:85
System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +208
System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +89
System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +78
System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +199
System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +107
System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +291
System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +13
System.Web.Mvc.<>c_DisplayClass1c.b_19() +23
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func1 continuation) +264
System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b() +20
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList1 filters, ActionResult actionResult) +176
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +329
System.Web.Mvc.Controller.ExecuteCore() +115
System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +94
System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10
System.Web.Mvc.<>c_DisplayClassb.b_5() +37
System.Web.Mvc.Async.<>c_DisplayClass1.b_0() +21
System.Web.Mvc.Async.<>c_DisplayClass81.<BeginSynchronous>b__7(IAsyncResult _) +12
System.Web.Mvc.Async.WrappedAsyncResult1.End() +55
System.Web.Mvc.<>c_DisplayClasse.b_d() +31
System.Web.Mvc.SecurityUtil.b_0(Action f) +7
System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +23
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +59
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8970061
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Answer 1

Here:
EditableHelpers.cs:90
I guess you are using some NuGet or something that depends on WebPages 2.0 (a.k.a System.Web.WebPages, Version=2.0.0.0). You probably updated this NuGet or whatever it is and now you have dependency with this assembly.