When I drag the .mp4 files from my video camera into movie maker, they all end up as X's with an error message about not understanding the format. However, they play fine in Media Player. Now what?
Answered at Best utility for converting Flip Mino HD videos to Windows Movie Maker compatible format? which suggested
SUPER © (Simplified Universal Player Encoder & Renderer)
MPEG Streamclip: video converter for Mac & Windows