YouTube and Vimeo are always changing the settings for their online interfaces, so it's pretty common -- especially when you're using older versions of the program -- to have the direct upload feature stop working.
When that happens, you can still output your video and upload it to these sites manually. Version 10 and later have an excellent tool for outputting AVC/MP4 video, which is perfect for uploading to these sites. Version 9 offers WMVs. The rest of the outputs are interlaced (including MPEGs), which don't look good online.
If you know what you're doing, you can create a custom preset for Quicktime/MOV that uses the H.264 preset and progressive rather than interlaced frames. That would be the ideal option for outputting a 1280x720 video.
I'm having the same problem but trying to upload as an MP4 to either you tube or Vimeo is taking in excess of 36 hours. Any hints?
If it's taking hours to upload a short MP4 to YouTube, the issue is either with your internet connection or YouTube.