Are you sure you have Windows version of MBII Launcher, not Linux version?
Try redownloading it by this link: http://www.moviebattles.org/download/MBIILauncher.exe
Are you sure you do have .NET 4.0?
.NET 4.5 (and above), and .NET 4.0 are different versions of .NET.
For Movie Battles, .NET 4.0...