Created On:  16 December 2010


An ASP.NET web application builds succesfully in Visual Studio but when trying to run or debug the application strange compiler error messages occur which point to source code in the App_Code subfolder or in temporary files.


The problem you are seeing is because you have an App_Code folder, which gets compiled at run-time and is only expected to be part of a Web Site, not a Web Application which is precompiled.

What is happening is that the contents of the project, including the classes in App_Code, get built to an assembly but at run-time the ASP.NET server
is compiling the contents of App_Code and specifying references to all of the project references plus the project output.

That means that the compiler is attempting to compile classes with a reference to compiled versions of themselves and not surprisingly it is getting rather confused hence the strange error messages.

If you rename your App_Code folder to a different name then the Web Project will run.