A couple things:
- Movie Maker 2.6 is a very old version of Movie Maker. It doesn't handle many video types (specifically .mov and .mp4) so that's probably the problem.
- The latest version is Movie Maker 2012 (ver 16.4) which you should download and install. It handles many more types of video, uses your GPU, has the ability to place text where you want, etc.
Movie Maker 2012 is part of Windows Essentials 2012.