The project you are trying to open was saved by a previous version of Visual Studio .NET. To use this version of Visual Studio ...

The project you are trying to open was saved by a previous version of Visual Studio .NET. To use this version of Visual Studio .NET, the project must be migrated to a new format. Once migrated, you will no longer be able to open the project in previous versions of Visual Studio .NET. Click ‘Yes' to migrate the project and its projects, click ‘No' to cancel the loading of the project.