The msvc projects for the sample extension should have been deleted from the repository as they are outdated and unsupported.
The included
ambuild files should be used instead for compiling (which can also generate msvc proj files for editing, if wanted). Additionally, you probably want to be compiling against stable SM (the 1.7-dev branch at time of writing), unless you want to be running unstable SM on the server on which you wish to run the extension.