Your DefaultAppPool is that set to the correct .net version (and managed pipeline mode) ?

From your log:

File name: 'System.Net.Http.Formatting, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' ---> System.IO.FileNotFoundException: Could not load file or assembly 'System.Net.Http.Formatting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

I think the assembly bindings are missing or wrong in your web.config, they should look like:

<runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">

        <!-- Old asp.net ajax assembly bindings -->
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="4.0.0.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="4.0.0.0" />
        </dependentAssembly>

        <!-- Ensure correct version of MVC -->
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Web.WebPages.Razor" publicKeyToken="31bf3856ad364e35" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
        </dependentAssembly>

        <!-- Ensure correct version of HtmlAgilityPack -->
        <dependentAssembly>
            <assemblyIdentity name="HtmlAgilityPack" publicKeyToken="bd319b19eaf3b43a" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-1.4.9.0" newVersion="1.4.9.0" />
        </dependentAssembly>

        <dependentAssembly>
            <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral"/>
            <bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.0.0.0"/>
        </dependentAssembly>

        <dependentAssembly>
            <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0" />
        </dependentAssembly>

        <dependentAssembly>
            <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-5.2.3.0" newVersion="5.2.3.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Web.Http" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-5.2.3.0" newVersion="5.2.3.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="Microsoft.Owin" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="Microsoft.Owin.Security.OAuth" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="Microsoft.Owin.Security" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="Microsoft.Owin.Security.Cookies" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Net.Http.Formatting" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-5.2.3.0" newVersion="5.2.3.0" />
        </dependentAssembly>

    </assemblyBinding>
</runtime>

My appPool looks like this:

And my bindings are looking exactly like yours.

I'm running on IIS 8.5

And those assemblies it is complaining about are in the bin dir?

Hmm mind checking the permissions on the bin folder then

Same on web.config?

Ok and your app pool runs as one of the identities that have access?

Great a step forward :) is there a valid connectionstring in the web.config ?

Seems the error you are getting now is

A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.

Thanks a lot for your help guys.

Apparently, I'm not quite out of the woods yet.

All problems where gone, in the back end. But my fronted still fails, like this.

And here is the log file from the Event Viewer: https://www.dropbox.com/s/3i53e91k1d31d1a/event-error3.txt?dl=0

If I remove 'Microsoft.Web.Helpers.dll' from the 'bin', the backend works flawlessly, but the frontend still fails.

I had the exact same problem, but solved it by updating ~/Views/web.config, which for some reason still contained a reference to Microsoft.Web.Helpers:

  <system.web.webPages.razor>
    <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    <pages pageBaseType="System.Web.Mvc.WebViewPage">
      <namespaces>
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
        <add namespace="Umbraco.Web" />
        <add namespace="Umbraco.Core" />
        <add namespace="Umbraco.Core.Models" />
        <add namespace="Umbraco.Web.Mvc" />
        <add namespace="Microsoft.Web.Helpers" /><!-- PROBLEM HERE -->
        <add namespace="umbraco" />
        <add namespace="Examine" />
      </namespaces>
    </pages>
  </system.web.webPages.razor>

Replacing this file with the one from the 7.3.7 zip-download solved the problem.

(It explains why the backend works - it does not render any of your views, which the frontend does!)

I hope that solves your problem, too! It took me three hours to track down...

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