Projects built with ASP.NET MVC are what are known as "flavored projects." This means that instead of being an entirely new project type, ASP.NET MVC projects merely extend a different kind of existing project type. Specifically, the projects extend the Web Application Project type.
If you try to open a flavored project and don't have that particular flavored project system installed, you get to see this little slice of heaven:
If you select "OK" then Visual Studio will continue, but the project will not be loaded:
Well, then, what do you do to continue? All you have to do is edit the project file to remove the flavoring. Right-click on the project, and select "Edit MyProjectName.vbproj".
This will launch Visual Studio's project file editor (with Intellisense, in case you didn't know!). Towards the top you'll see a list of project types associated with this project, each one represented by a GUID.
<ProjectTypeGuids>{603c0e0b-db56-11dc-be95-000d561079b0};{349c5851-65df-11da-9384-00065b846f21};{F184B08F-C81C-45F6-A57F-5ABD9991F28F}</ProjectTypeGuids>
The first GUID there (the one that starts with "603c") is the one used by ASP.NET MVC projects. Remove that GUID so you end up with:
<ProjectTypeGuids>{349c5851-65df-11da-9384-00065b846f21};{F184B08F-C81C-45F6-A57F-5ABD9991F28F}</ProjectTypeGuids>
Save the project file and close it.
Now reload the project:
And you'll be able to work on the project once again. The only thing you won't be able to use is MVC project-specific features such as the "Add View" menu option.
I find myself doing this very often since my work machine is always in a bizarre state with respect to ASP.NET MVC and I often don't have the project type installed. This is much faster than trying to install MVC just so I can inspect a project.