Whereabouts is it saying invalid file? In the TechCrunch site? Ok, try these steps:
1. Goto http://mytube.kuso.cc/~kuso/youtube/
2. Enter the YouTube link into the box there
3. Click Download Link and download the YouTube movie in .FLV format
4. Get this program : http://www.dvdvideosoft.com/products/dvd/Free-YouTube-to-iPod-Converter.htm - or a direct link to the file here - http://www.dvdvideosoft.com/download/FreeYouTubeToiPodConverter.exe
5. Convert the .FLV to .MP4 using that program, it's really simple to convert, just open the .FLV file in it, and click Convert.
Good luck!