After following the standard upgrade path found on Upgrades in general and stepping through the all the configs in the config folder as well as the base web.config AND the views/web.config via WinMerge; I restarted the site profile, opened the site in Chrome, and was walked through the upgrade steps as usual!

I'm thinking then "YAY this site can go live once I push these changes to the production server and go to bed!!!"

Once the upgrade completed I went into the back office and republished the entire site just to be on the safe side. I sat back, relaxed and opened the site front end ... to receive a YSOD!

Server Error in '/' Application.

The controller for path '/' was not found or does not implement IController.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Web.HttpException: The controller for path '/' was not found or does not implement IController.

Source Error: 


Line 41:        }
Line 42:                <header>
Line 43:                    @Html.Action("PrepareCallback", "CallbackFormSurface")
Line 44:                    <p id="helplineCallbackResponse"></p>
Line 45:                </header>

Source File: e:\sites\WIP\www.lawcare.org.uk\website\Views\Partials\Hotlines.cshtml    Line: 43 

Stack Trace: 


[HttpException (0x80004005): The controller for path '/' was not found or does not implement IController.]
   System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +683953
   Umbraco.Web.Mvc.RenderControllerFactory.CreateController(RequestContext requestContext, String controllerName) +162
   System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +305
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +87
   System.Web.Mvc.ServerExecuteHttpHandlerWrapper.Wrap(Func`1 func) +41

[HttpException (0x80004005): Execution of the child request failed. Please examine the InnerException for more information.]
   System.Web.Mvc.ServerExecuteHttpHandlerWrapper.Wrap(Func`1 func) +785864
   System.Web.HttpServerUtility.ExecuteInternal(IHttpHandler handler, TextWriter writer, Boolean preserveForm, Boolean setPreviousPage, VirtualPath path, VirtualPath filePath, String physPath, Exception error, String queryStringOverride) +3977
   System.Web.HttpServerUtility.Execute(IHttpHandler handler, TextWriter writer, Boolean preserveForm, Boolean setPreviousPage) +275
   System.Web.HttpServerUtilityWrapper.Execute(IHttpHandler handler, TextWriter writer, Boolean preserveForm) +94
   System.Web.Mvc.Html.ChildActionExtensions.ActionHelper(HtmlHelper htmlHelper, String actionName, String controllerName, RouteValueDictionary routeValues, TextWriter textWriter) +700
   System.Web.Mvc.Html.ChildActionExtensions.Action(HtmlHelper htmlHelper, String actionName, String controllerName, RouteValueDictionary routeValues) +123
   ASP._Page_Views_Partials_Hotlines_cshtml.Execute() in e:\sites\WIP\www.lawcare.org.uk\website\Views\Partials\Hotlines.cshtml:43
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +280
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +126
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +196
   StackExchange.Profiling.MVCHelpers.WrappedView.Render(ViewContext viewContext, TextWriter writer) +295
   System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData) +158
   Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, CacheItemPriority priority, CacheItemRemovedCallback refreshAction, CacheDependency cacheDependency, Nullable`1 timeout, Func`1 getCacheItem, Object syncLock) +218
   Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, CacheItemPriority priority, CacheItemRemovedCallback refreshAction, CacheDependency cacheDependency, Nullable`1 timeout, Func`1 getCacheItem) +176
   Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, CacheItemPriority priority, CacheItemRemovedCallback refreshAction, Nullable`1 timeout, Func`1 getCacheItem) +154
   Umbraco.Web.CacheHelperExtensions.CachedPartialView(CacheHelper cacheHelper, HtmlHelper htmlHelper, String partialViewName, Object model, Int32 cachedSeconds, String cacheKey, ViewDataDictionary viewData) +438
   Umbraco.Web.HtmlHelperRenderExtensions.CachedPartial(HtmlHelper htmlHelper, String partialViewName, Object model, Int32 cachedSeconds, Boolean cacheByPage, Boolean cacheByMember, ViewDataDictionary viewData) +428
   ASP._Page_Views_SW_Master_cshtml.Execute() in e:\sites\WIP\www.lawcare.org.uk\website\Views\SW_Master.cshtml:118
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +280
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +126
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +196
   System.Web.WebPages.WebPageBase.Write(HelperResult result) +89
   System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName, Action`1 body) +233
   System.Web.WebPages.WebPageBase.PopContext() +291
   StackExchange.Profiling.MVCHelpers.WrappedView.Render(ViewContext viewContext, TextWriter writer) +295
   System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +378
   System.Web.Mvc.<>c__DisplayClass1a.<InvokeActionResultWithFilters>b__17() +33
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +854204
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +854204
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +265
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +854256
   System.Web.Mvc.<>c__DisplayClass1d.<BeginExecuteCore>b__19() +40
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +15
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +65
   System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +15
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +51
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__3(IAsyncResult asyncResult) +42
   System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +15
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +51
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +606
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +288

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.17929

So here is the offending line 43 of "Hotlines.cshtml":

@Html.Action("PrepareCallback", "CallbackFormSurface")

And here is the Surface Controller (found in the "App_Code" directory atm):

using System;
using System.ComponentModel.DataAnnotations;
using System.Net.Mail;
using System.Text;
using System.Web.Mvc;
using Umbraco.Web;
using Umbraco.Web.Mvc;

/// <summary>
/// Summary description for HotlineController
/// </summary>
public class CallbackFormSurfaceController : SurfaceController
{
[ChildActionOnly]
public ActionResult PrepareCallback()
{
    TempData.Clear();

    return PartialView("CallbackForm", new CallbackFormModel
    {
        CallbackHeadline = CurrentPage.AncestorOrSelf(1).GetPropertyValue<string>("callbackHeadline"),
        CallbackPlaceholder = CurrentPage.AncestorOrSelf(1).GetPropertyValue<string>("callbackPlaceholder"),
        CallbackTooltip = CurrentPage.AncestorOrSelf(1).GetPropertyValue<string>("callbackTooltip"),
        CallbackButtonText = CurrentPage.AncestorOrSelf(1).GetPropertyValue<string>("callbackButtonText")
    });
}


[HttpPost]
public ActionResult RequestCallback(CallbackFormModel model)
{
    String fieldError = String.Empty;
    var member = umbraco.cms.businesslogic.member.Member.GetCurrentMember();
    StringBuilder fieldErrorString = new StringBuilder();

    var recipientProp = CurrentPage.AncestorOrSelf(1).GetProperty("callbackRecipient");
    var senderProp = CurrentPage.AncestorOrSelf(1).GetProperty("callbackSender");
    var subjectProp = CurrentPage.AncestorOrSelf(1).GetProperty("callbackSubject");
    var responseProp = CurrentPage.AncestorOrSelf(1).GetProperty("callbackResponse");
    var responsePage = CurrentPage.AncestorOrSelf(1).GetProperty("callbackRedirection");


    if (recipientProp == null || recipientProp.Value == null || recipientProp.Value.ToString().Length == 0)
    {
        fieldError = "The 'Callback Recipient Email Address' property has not been completed";
        fieldErrorString.AppendLine(fieldError);
        if (member != null) throw new MissingFieldException(fieldError);
    }

    if (senderProp == null || senderProp.Value == null || senderProp.Value.ToString().Length == 0)
    {
       fieldError = "The 'Callback Sender Email Address' property has not been completed";
       fieldErrorString.AppendLine(fieldError);
       if (member != null) throw new MissingFieldException(fieldError);
    }
    if (subjectProp == null || subjectProp.Value == null || subjectProp.Value.ToString().Length == 0)
    {
        fieldError = "The 'Callback Subject Line' property has not been completed";
        fieldErrorString.AppendLine(fieldError);
        if (member != null) throw new MissingFieldException(fieldError);
    }

    if (responseProp == null || responseProp.Value == null || responseProp.Value.ToString().Length == 0)
    {
        fieldError = "The 'Callback Thank You Message' property has not been completed";
        fieldErrorString.AppendLine(fieldError);
        if (member != null) throw new MissingFieldException(fieldError);
    }

    if (responsePage == null || responsePage.Value == null || responsePage.Value.ToString().Length == 0)
    {
        fieldError = "The 'Callback Thank You Page' property has not been completed";
        fieldErrorString.AppendLine(fieldError);
        if (member != null) throw new MissingFieldException(fieldError);
    }



    if (!ModelState.IsValid)
    {
        String errorMessage = "Oops! We've hit a small glitch but the site admins have been notified at " + DateTime.Now + ". Please ring us directly at your earliest convenience.";
        TempData.Add("Status", errorMessage );
        SendErrorReport("[email protected]", "website.lawcare.org.uk", "[email protected]",
                               "Callback Form Error.", fieldErrorString.ToString(), CurrentPage.Name);
        model.ShowForm = false;
        model.ShowMessage = true;
        return CurrentUmbracoPage();
    } 

    //SendSmtpEmail(recipientProp.Value.ToString(), senderProp.Value.ToString(), "[email protected]", subjectProp.Value.ToString(), model);

    SendSmtpEmail("[email protected]", senderProp.Value.ToString(), "[email protected]", subjectProp.Value.ToString(), model);

    model.ShowForm = false;
    model.ShowMessage = true;


    //return RedirectToCurrentUmbracoPage();
    //return CurrentUmbracoPage();
    return RedirectToUmbracoPage(Convert.ToInt32(responsePage.Value));
}

private void SendSmtpEmail(string recipientEmail, string senderEmail, string adminEmail, string subjectLine, CallbackFormModel model)
{
    StringBuilder body = new StringBuilder();
    body.AppendLine(subjectLine);
    body.AppendLine();
    body.AppendLine("Requesters Phone Number: " + model.CallbackPhoneNumber);
    body.AppendLine();
    body.AppendLine("Regards,");
    body.AppendLine("Lawcare Website Robot");


    MailMessage internalMessage = new MailMessage();
    internalMessage.To.Add(new MailAddress(recipientEmail));
    internalMessage.From = new MailAddress(senderEmail);
    internalMessage.Bcc.Add(new MailAddress(adminEmail));
    internalMessage.Body = body.ToString();
    internalMessage.Subject = subjectLine + ": " + CurrentPage.Name;
    internalMessage.IsBodyHtml = false;

    SmtpClient smtpInternal = new SmtpClient();
    smtpInternal.Send(internalMessage);

 }


private void SendErrorReport(String emailTo, String emailFrom, String emailBcc, String emailSubject, String emailMessage, String errorLocation)
{
    StringBuilder body = new StringBuilder();
    body.AppendLine(emailSubject);
    body.AppendLine();
    body.AppendLine("Error: " + emailMessage);
    body.AppendLine();
    body.AppendLine("Regards,");
    body.AppendLine("Lawcare Website Robot");


    MailMessage internalMessage = new MailMessage();
    internalMessage.To.Add(new MailAddress(emailTo));
    internalMessage.From = new MailAddress(emailFrom);
    internalMessage.Bcc.Add(new MailAddress(emailBcc));
    internalMessage.Body = body.ToString();
    internalMessage.Subject = emailSubject + ": " + errorLocation;
    internalMessage.IsBodyHtml = false;

    SmtpClient smtpInternal = new SmtpClient();
    smtpInternal.Send(internalMessage);

}

}

public class CallbackFormModel
{
    public bool ShowMessage { get; set; }
    public bool ShowForm { get; set; }

    public string CallbackFormIdentity { get; set; }
    public string CallbackHeadline { get; set; }
    public string CallbackPlaceholder { get; set; }
    public string CallbackTooltip { get; set; }
    public string CallbackButtonText { get; set; }

    public string UpdateTargetBox { get; set; }

    [Required(AllowEmptyStrings = false, ErrorMessage = "Please enter your phone number")]
    [Display(Name = "We can also call you", Prompt = "Your Phone Number")]
    [DataType(DataType.PhoneNumber)]
    public string CallbackPhoneNumber { get; set; }
}

Have I done something wrong in the upgrade or what?

As always all help is greatly appreciated and I can give access to files or anything else if need be!

Thank you for your time and patience!

Jon @precisioncoding