I'm also using Win 7 and I've run into a similar issue. Try the following steps:
1.) Unpack the downloaded msi-zip
2.) Right-click on the required dll and choose "Properties"
3.) Check if there is a security warning at the bottom such as "file came from another computer and might be dangerous".
4.) Click on "Unblock" and confirm.
Note: If this file has been placed into a "secured" area such as "program files" the unblock-command will not be stored permanently! You'd have to move it someplace else and unblock it there first.
5.) Try again to reference the file.
Visual Studio doesn't seem to like importing "blocked" files >.<