Dear Victor,
it might depend on some small details of the avi format. If you run:
Export["~/Desktop/movie.avi", Table[Plot[Sin[\[Omega] t], {t, 0, 10}], {\[Omega], 0.1, 2, 0.1}]]
Import["~/Desktop/movie.avi", "Animation"]
it does appear to work. I have noticed that importing avi does sometimes cause problems. I then usually convert them to gif and use those. Gif rarely causes problems.
Cheers,
Marco