do an f1 search on shadow maps and depth maps - it will give you a better explanation than i can. as for the cast shadows option, just select the object, open up the attribute editor and look under render stats. you may want to also try starting from scratch and create a new light. sometimes it's better to just start again, rather than try to work out what you're missing. as i said, post up your lights attribute editor so we can take a look at your options.