I'm glad that it worked for you. The reason why you shouldn't render to .avi is because if anything happens during you render, say Maya crashes, your avi will never get created. Now imagine that your computer has been rendering for like a day or two and you lose everything during the last 10 min. I promise you wont be happy .

If you render to images and Maya crashes you will still have everything left that you rendered before the crash. All you have to do then is continue the render from where it stopped.