Before going into the solution let us understand that whats the difference between Classic mode and Integrated mode.
Classic mode cannot interact with the IIS pipeline whereas Integrated mode can interact directly with the IIS pipeline.
In Classic mode IIS works only with ISAPI extensions (as IIS 6). When using classic mode the server uses two pipeline to handle requests, one for native code and one for managed code. In Integrated mode, IIS handles all requests through a unified pipeline which is tightly integrated with ASP.Net through the same pipeline. So in simple terms, Classic mode works the same way as ASP.NET has worked on previous versions of IIS.
The solution of this problem is shown in the error page itself, below "Things you can try".
Firstly, you can change Managed Pipeline Mode from Integrated to Classic as below. Problem with moving to Classic Mode will make your application unable to take advantage of ASP.NET improvements made possible in Integrated mode.
Or, you can make validateIntegratedModeConfiguration="false" in web.config as shown below
Please Like and Share the Blog, if you find it interesting and helpful.