Snow falling effect

Hi guys…

Just wondering if anyone would know how to solve my problem… Im following the kirupa create falling snow tutorial and my document size is 500 x 400 and every few seconds it does a jerking motion… not a continous snow falling effect… thnks :te: Also, although i have put a stop action the snow keeps continously playing, i only want this snow falling action to play in one scene… plse help. anybody?