Breaking Changes in asp.net MVC Preview

The following changes might cause errors in existing ASP.NET MVC 1.0 applications.

Installing ASP.NET MVC 2 Preview 2 Alongside ASP.NET MVC 1.1

The runtime component of ASP.NET MVC is shared by Visual Studio 2008 and Visual Studio 2010. If you have ASP.NET MVC 1.1 installed, you must uninstall it before you install ASP.NET MVC 2 Preview 2. Use the following steps to uninstall ASP.NET MVC 1.1 and install ASP.NET MVC 2:

1. From the Windows Control Panel, open Add/Remove Programs.

2. Uninstall Microsoft Visual Studio 2010 Tools for ASP.NET MVC 1.1

3. Uninstall Microsoft ASP.NET MVC 1.1

4. Install ASP.NET MVC 2

NGen Priority Change

When System.Web.Mvc.dll is installed in the Global Assembly Cache (GAC), the installer also invokes the NGen service to generate a native image. In previous versions of the installer, the service was invoked with a service request priority of 0, which caused the installer to create a native image immediately as part of the setup process. Many customers have reported problems where the NGen service fails, forcing the installation of MVC to be rolled back. These failures can usually be attributed to missing assemblies or corrupt entries inside the registry hive that is maintained by the CLR. However, the cost for customers is that they cannot install MVC until these issues have been addressed.

Starting with MVC 2 Preview 2, all the assemblies for which native images are created are queued by lowering the priority of the service request to 3. This will allow the installation of MVC to complete even if other problems arise, because native images for System.Web.Mvc.dll will be created only when the system is idle after the installation process.