You really need to get a Book on Flex, There are alot of things wrong with your code. What you mention is not an error but a warning. It mean when that variable changes the data binding framwork will not be able to show those changes. You need to tag the variable with a [Bindable] metadata. You need a good flex book.
Data binding will not be able to detect assignments to "chartData".
Just a little tip, this should be your post headline, instead of "Help with code".
This is what you are missing. But, it might not be the best way to do what you want to do.
[Binable] private var chartData:ArrayCollection = new ArrayCollection;
You probably should find an example on the web before trying stuff and keep trying the example until you get it working yourself.