MVC 3 Stops working after MVC4 Installation [duplicate]

Question

Possible Duplicate:
MVC 4 Beta side by side installation error

I have an MVC3 application in progress. I want to start another application in MVC4. But MVC 3 application stopped working after MVC 4 installation(not beta). getting some dll conflicting errors. One of the error is like this.

The type 'System.Web.Helpers.Json' exists in both 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL    \System.Web.Helpers\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.Helpers.dll' and 'c:\Windows    \Microsoft.NET\assembly\GAC_MSIL\System.Web.Helpers    \v4.0_1.0.0.0__31bf3856ad364e35\System.Web.Helpers.dll' `at      System.Web.Compilation.AssemblyBuilder.Compile()
   at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
   at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean    noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean    ensureIsUpToDate)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context,    VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile,    Boolean throwIfNotFound, Boolean ensureIsUpToDate)
   at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath,    HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound)
   at System.Web.Compilation.BuildManager.GetObjectFactory(String virtualPath, Boolean throwIfNotFound)
   at System.Web.Mvc.BuildManagerWrapper.System.Web.Mvc.IBuildManager.FileExists(String virtualPath)
   at System.Web.Mvc.BuildManagerViewEngine.FileExists(ControllerContext controllerContext, String   virtualPath)
   at System.Web.Mvc.VirtualPathProviderViewEngine.GetPathFromGeneralName(ControllerContext controllerContext, List`1 locations, String name, String controllerName, String areaName, String cacheKey, String[]& searchedLocations)
   at System.Web.Mvc.VirtualPathProviderViewEngine.GetPath(ControllerContext controllerContext, String[] locations, String[] areaLocations, String locationsPropertyName, String name, String controllerName, String cacheKeyPrefix, Boolean useCache, String[]& searchedLocations)
   at System.Web.Mvc.VirtualPathProviderViewEngine.FindView(ControllerContext controllerContext, String viewName, String masterName, Boolean useCache)
   at System.Web.Mvc.ViewEngineCollection.<>c__DisplayClassc.<FindView>b__b(IViewEngine e)
   at System.Web.Mvc.ViewEngineCollection.Find(Func`2 lookup, Boolean trackSearchedPaths)
   at System.Web.Mvc.ViewEngineCollection.Find(Func`2 cacheLocator, Func`2 locator)
   at System.Web.Mvc.ViewEngineCollection.FindView(ControllerContext controllerContext, String viewName, String masterName)
   at System.Web.Mvc.ViewResult.FindView(ControllerContext context)
   at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult)
   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)`

what would be a fix for this?

Answer 1

I found the solution here

Installing ASP.NET MVC 4 breaks ASP.NET MVC 3 RTM applications. ASP.NET MVC 3 applications that were created with the RTM release (not with the ASP.NET MVC 3 Tools Update release) require the following changes in order to work side-by-side with ASP.NET MVC 4. Building the project without making these updates results in compilation errors. Required updates

In the root Web.config file, add a new entry with the key webPages:Version and the value 1.0.0.0.

<appSettings>
<add key="webpages:Version" value="1.0.0.0"/>
<add key="ClientValidationEnabled" value="true"/>
<add key="UnobtrusiveJavaScriptEnabled" value="true"/>
</appSettings>

In Solution Explorer, right-click the project name and then select Unload Project. Then right-click the name again and select Edit ProjectName.csproj. Locate the following assembly references:

<Reference Include="System.Web.WebPages"/> 
<Reference Include="System.Web.Helpers" />

Replace them with the following:

<Reference Include="System.Web.WebPages, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL "/> 
<Reference Include="System.Web.Helpers, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />

Save the changes, close the project (.csproj) file you were editing, and then right-click the project and select Reload.

(You can manually edit the MVC project file in text editor also. Right click the .csproj file and open with any text editor and edit carefully the xml)