Youtube wont let me upload my video?

I was trying to upload videos from my canon powershot g11 to youtube, but it didn't work. So, I converted it to .flv file, but when I tried to upload it again it says ERROR. Does anyone know what is wrong?!
Update: Well I tried some of these suggestions, and I kept on converting it and still didn't work. But when I tried uploading it on youtube mobile it worked, weird..
Update 2: Oh! And thanks for all these answers!
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