Method Last Problem

Hi, having an issue with the last method. I have a list called ballList which contains a list of TBall types. I'm trying to get the last TBall in the list using the following:

Local tempBall:TBall
tempBall = ballList.last()

However, when I build it says 'Unable to convert from Object to TBall'

Sorry, but just cant see what I'm doing wrong - other examples seem to suggest I'm using this correctly! Can anyone help?
thanks guys