Sitecore.Mvc.Analytics exception For A/B Testing

Question

I'm trying to perform a simple A/B test.
There is a layout that has only one placeholder.

<div>
    @Html.Sitecore().Placeholder("main") //breakpoint here which throws exception
</div>

Then there is a view rendering (called Section) with a datasource that has to load inside the placeholder. By default, Section is assigned a datasource item Text1. I can view the desired result in Experience editor.
Now, I add another variation, by just changing the datasource for the same rendering to Text2. I can see in the floating box, the two variations and the text being changed when manually changing the variations.
I click on Save and try to open the page again in Experience editor and there is this exception.

An exception of type 'System.NullReferenceException' occurred in Sitecore.Mvc.Analytics.dll but was not handled in user code

I am unable to view this page in Experience editor now after adding the second variation.
The page is assgined the sitecore's Sample workflow. I have also added Sitecore.Analytics.dll & Sitecore.Mvc.Analytics.dll to the Visual Studio solution.

How to fix this?
Using Sitecore 8.2 with VS2015

Error Log I checked the error log which at a point says something about the layout. The layout exists and other pages using the same layout work fine. The problem occurs after adding a second variation and viewing in exp. editor. It works ok when viewing in preview mode !!

Here is the log recorded. Hope it tells something......

ManagedPoolThread #11 10:40:21 INFO Job ended: Sitecore.ListManagement.Analytics.UnlockContactListsAgent (units processed: )
12968 10:40:28 ERROR Application error.
Exception: System.Web.HttpUnhandledException
Message: An unhandled exception occurred.
Source: Sitecore.Mvc
at Sitecore.Mvc.Pipelines.MvcEvents.Exception.ShowAspNetErrorMessage.ShowErrorMessage(ExceptionContext exceptionContext, ExceptionArgs args)
at Sitecore.Mvc.Pipelines.MvcEvents.Exception.ShowAspNetErrorMessage.Process(ExceptionArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Filters.PipelineBasedRequestFilter.OnException(ExceptionContext exceptionContext)
at System.Web.Mvc.ControllerActionInvoker.InvokeExceptionFilters(ControllerContext controllerContext, IList`1 filters, Exception exception)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
at Sitecore.Mvc.Controllers.SitecoreActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
at System.Web.Mvc.Controller.<>c__DisplayClass22.<BeginExecuteCore>b__1e()
at System.Web.Mvc.Async.AsyncResultWrapper.<.cctor>b__0(IAsyncResult asyncResult, Action action)
at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
at Sitecore.Mvc.Routing.RouteHttpHandler.EndProcessRequest(IAsyncResult result)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Nested Exception

Exception: System.InvalidOperationException
Message: Error while rendering view: '/Views/CampaignLayout.cshtml' (model: 'Sitecore.Mvc.Presentation.RenderingModel, Sitecore.Mvc').

Source: Sitecore.Mvc
at Sitecore.Mvc.Presentation.ViewRenderer.Render(TextWriter writer)
at Sitecore.Mvc.Pipelines.Response.RenderRendering.ExecuteRenderer.Render(Renderer renderer, TextWriter writer, RenderRenderingArgs args)
at Sitecore.Mvc.Pipelines.Response.RenderRendering.ExecuteRenderer.Process(RenderRenderingArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Presentation.RenderingView.Render(ViewContext viewContext, TextWriter writer)
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)

Nested Exception

Exception: System.NullReferenceException
Message: Object reference not set to an instance of an object.
Source: Sitecore.Mvc.Analytics
at Sitecore.Mvc.Analytics.Pipelines.Response.CustomizeRendering.SelectVariation.GetTestCombination(Item variableItem, Item contextItem, ID deviceId)
at Sitecore.Mvc.Analytics.Pipelines.Response.CustomizeRendering.SelectVariation.GetVariation(Item variableItem, Item contextItem, ID deviceId)
at Sitecore.Mvc.Analytics.Pipelines.Response.CustomizeRendering.SelectVariation.Evaluate(CustomizeRenderingArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs,TResult](String pipelineName, TArgs args, Func`2 resultGetter)
at Sitecore.Mvc.Analytics.Pipelines.Response.GetRenderer.CustomizeRendering.Process(GetRendererArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs,TResult](String pipelineName, TArgs args, Func`2 resultGetter)
at Sitecore.Mvc.Presentation.Rendering.GetRenderer()
at Sitecore.Mvc.Presentation.Rendering.get_Renderer()
at Sitecore.Mvc.Presentation.Rendering.ToString()
at Sitecore.Mvc.Pipelines.Response.RenderRendering.InitializeProfiling.StartProfiling(RenderRenderingArgs args)
at Sitecore.Mvc.Pipelines.Response.RenderRendering.InitializeProfiling.Process(RenderRenderingArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Pipelines.Response.RenderPlaceholder.PerformRendering.Render(String placeholderName, TextWriter writer, RenderPlaceholderArgs args)
at (Object , Object[] )
at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
at Sitecore.Mvc.Pipelines.PipelineService.RunPipeline[TArgs](String pipelineName, TArgs args)
at Sitecore.Mvc.Helpers.SitecoreHelper.Placeholder(String placeholderName)
at ASP._Page_Views_CampaignLayout_cshtml.Execute() in c:\inetpub\wwwroot\democore\Website\Views\CampaignLayout.cshtml:line 45
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData)
at Sitecore.Mvc.Presentation.ViewRenderer.Render(TextWriter writer)



12968 10:40:28 INFO Cache created: 'Log singles' (max size: 100KB, running total: 2297MB)
12968 10:40:28 WARN Page extenders were not added, because an error occurred during the request execution
ManagedPoolThread #6 10:40:31 INFO Job started: Sitecore.ListManagement.Analytics.UnlockContactListsAgent
ManagedPoolThread #6 10:40:31 INFO Job ended: Sitecore.ListManagement.Analytics.UnlockContactListsAgent (units processed: )
ManagedPoolThread #7 10:40:41 INFO Job started: Sitecore.ListManagement.Analytics.UnlockContactListsAgent
ManagedPoolThread #7 10:40:41 INFO Job ended: Sitecore.ListManagement.Analytics.UnlockContactListsAgent (units processed: )