[SIZE=-0] What does "Invalid file format error" mean? [/SIZE]
"Invalid file format error" means that your video is in a format that our system doesn't accept. We accept most file formats, including .wmv, .mov, .mpg, or .avi. If your video meets these minimum requirements and still won't upload, it may be due to a problem with the video compression you are using. We recommend the MPEG4 (Divx, Xvid, SVQ3) format at 320x240 resolution with MP3 audio. Resizing your video to these specifications before uploading will help your clips look better on YouTube.
If you're using Windows Movie Maker, it's also possible that you tried to upload your .MSWMM file. This is not an actual movie file. An .MSWMM file is a Windows Movie Maker project file. If you're satisfied with your movie, choose the "Publish Movie" or "Save Movie File" option (depending on which version you have) under the "File" menu and create a movie file such as .avi or .wmv.