.NET Framework 4 and Could Not Load Type ‘System.ServiceModel.Activation.HttpModule’ Error …

  So, day before yesterday I was working on some app. And I deployed it on my IIS (v7.5) server. The deployment process went very well without any sort of troubles. But when I tried to run that application from my web browser I got loads of error. And I found that the main error

ASP.NET and Page Not Found Error while debugging !

Being sunny weekend today, with full of energy I began to work on making some prototype application which I have to present to my client sometimes during next week. It been a while since I worked on ASP.NET on my application (@ 2 weeks) since I installed Sharepoint Server 2010 demo in my machine. So,