如何在.NET 3.5 Web应用程序中使用.NET 4.0 Web应用程序？

My company has a website built in ASP.NET and targets .NET 3.5. It is too mangled and massive to be converted to .NET 4 in a timely manner. I am tasked with building a ticketing system. I want this ticketing system to be a completely separate application from the main application. I added a directory to the website called "TicketingSystem", then in IIS I set this folder as an application, using an app pool that targets .net 4.0. I assumed this application would not be affected by the application above it, especially since it uses its own app pool, but it would seem it is being affected somehow. Navigating to this directory with my .net 4 web app in it generates this error:My company has a website built in ASP.NET and t