Why won't Windows Live Movie Maker play wmv file?

I'm making a video using the Windows 7 Windows Live Movie Maker and I have a movie clip that's been converted to a .wmv file but when I place it on the timeline it gets the error saying "The file might be corrupted or in a format that Movie Maker doesn't recognize." But I have other video files before this one that are wmv and they work fine! What can I do? If you'd like to know, I'm making a Sonic the Hedgehog tribute memory type movie and I'm taking video clips from YouTube, downloading them using a YouTube downloader and then using that downloader to convert it to a WMV file. Please help!