I am not able to upload my iMovie video to youtube?

I am not able to upload my video created in iMovie11 to you tube. I have tried different extentsions, quickplayer, avi, mpeg, all to no avail. Are there any suggestionsn

I have generated similar video in Camtasia in Windows computer and it works fine. In imovie, you tube disconnects after a few minutes. Any help greatly appreciated?